Johnson, Evinrude, OMC, outboard motor, outboard motor repair, 9.9, 15 hp, date/year of manufacture, water pump, carburetor, long shaft, 15 hp conversion, sailmaster

  

 

These outboards, like any that get used & or abused may need to be torn apart & repaired over time.  As they get older, the depreciated value of a somewhat neglected/abused motor is such that with a motor in the 25 year old range, it could be questionable as to whether taking it to a outboard mechanic is worthwhile for other than electrical trouble shooting type of repairs.  Some shops even refuse to work on anything over 20 years old.  I have seem abused motors that I would not pay $50 for, & then again the next one that has been used but maintained, may be worth from $500 to $1000, depending on the year, compression, & whether it is electric start & a longshaft or not.  It is my observation that most outboard motor problems are not that the motor is worn out, but it is the NEGLECT / ABUSE  & lack of care it received over it's lifetime.  An older well cared for motor, is worth way more than a newer neglected / damaged motor.

This article is not meant to take the place of a service manual.  It however has some tips from my personal experiences & other information that has been gleaned from many sources over the years that may make owning and /or repairing your motor a little easier to understand.  Most commercial outboard mechanics have to work on many different makes & sizes of motors in order to make a living, therefore it is unreasonable to expect them to remember the whole history & the little extra things to look for when repairing one particular make & model.   Hopefully this article will help those of you who do decide to "DO IT YOURSELF".

If there is any chance that you do decide to work on it yourself, it is recommended that you purchase one of the excellent illustrated service manuals that covers your motor before you venture too far into trying to repair something you may not be that familiar with.  It is also highly recommended that you get a factory parts catalog for the year of motor in question.  This way you can see the exploded view of the parts & can order by part number. The part numbers may have been superseded, but the shop you go to when ordering parts, can cross-reference to the new number.  This parts manual also helps you positively identify the part you need, as compared to ordering something by the wrong name & getting the wrong part.  Remember, most of mechanics/counterpersons flunked mind-reading school.  These parts manuals will also provide a picture placement of the related parts.

One source of original or reproduction manuals would be to go to www.ebay.com & then type in outboard motor or 9.9 johnson as a search.  Used original OMC parts manuals for these motors usually go for from between $5 to $20 & are more in demand than the service manuals.    Original, or copies of OMC Service Manuals for the year motor you are working on would be best.  There may be some latitude as for years if it is close to what yours is, with the exception of the 74-76 electronics, being on their own.   Undoubtedly the parts manuals are very important to the home mechanic.  Another thing that can be invaluable is a digital camera.  If you tear it apart more than just to replace some small item, take a few pictures of the motor with the cowlings off. 

 

The service manuals are very helpful & explain in detail just how to repair the motor.  You really need both the service manual & the parts manual. 

Owners manuals do not really help you when doing repairs, they just give you pointers on how to adjust carburetor, the trim & how to jeep it clean.  

Also be aware that when you go to the dealer to order parts, that many times some of the larger dealers would rather you brought your motor in to them to work on.  Therefore they possibly may resist ordering parts for you saying they are hard to find.  Or if they do accept your order, they may not place your parts order at the top of the "To Order" priority list, since you are planning on doing the repairs yourself.   If you go to them with part numbers they may be more obliging to place an order, since the monkey is on your back for providing the right or wrong part numbers, & you are then obliged to pay for them even if some wrong parts show up.  However, if you do come up with your own numbers, also have the description, so they have some idea of what it is.  It would also be best to indicate which year of parts list you used, as many of these older parts numbers have been superseded by newer numbers.  

Another thing to consider is that most times the manufacturer or distributor like to have an order from the dealer in minimum quantity or dollar value to cut down on excess shipping.  There is the possibility that the dealer may have just placed an order & will not place another until they get enough accumulated to qualify for another order.  They will undoubtedly want you to prepay for the order.  Also when the order comes in, even though you requested them to call you, with possibly more than one person in the shop, that information may have gotten misplaced.  They should be able to give you an estimated delivery time.  However don't call them & inquire for at least for a couple of weeks.

I am not an outboard mechanic, but a semi-retired machinist who has been working on this series of motors exclusively for about 25 years.   If you are like me, & do not have anywhere near a photographic memory, by the time you tear it apart, get the parts ordered & then try to reassemble it weeks later, you can not really remember the exact sequence or placement of some critical parts.   Also someone else could have worked on it in the past & the part may not be where it actually belongs.   Most times you can figure it out by trial & error, but proper placement of others that may be somewhat internal, where if you guess wrong, may require the whole engine or lower unit to be disassembled again just to reposition or add one forgotten part, (been there-done that) which can be frustrating.  This miss-placement of a part will usually come to you some time later,  & usually in the middle of the night.  With the digital cameras commonly in use now, this may be a good way to record what things should look like before or while you take it apart.

This is Not Really a Trouble-Shooting Article :  You will find my troubleshooting article by itself.  In the following information provided in this article, it is assumed that the motor is in a good enough condition TO run.  If you have bad spark plugs, rings, carburetor being fouled, or anything that may contribute to the engine not running then you will need to address that situation, especially as a pre-requisite to doing anything else.  Any work needed should also be done in addition to what  is covered here.  AND, we are assuming that you have the motor mounted on the boat transom properly with the cavitaion plate even with the hull's bottom & the motor tilted at an angle that lets the cavitaion plate be straight with the bottom.

Free Advice : You may find persons who offer free advice on about any subject, outboard motors "experts" are no different, but I have found that MOST of these Good Samaritans may not be as good as they think they are.   Some like to talk just to try to impress people.  If you happen to frequent some of the boat or motor message boards, you will soon see a response to the question of a motor not running exactly right.  The most common response is to rebuild the carburetor.  OK, this may be part of the problem, but it is not the cure-all, as your problem could also be ignition or compression related.   Another response often seen is that you should replace the water pump impeller every 2 to 3 years, just a a precautionary measure.  This might be so, IF you are operating in VERY MUDDY, SANDY or debris infected water, OR are using it as in a main motor that is used many miles offshore.  The current new impellers should last for MANY years if the motor is treated right.   I replaced one of mine after 20 years, it was still intact & functioning as far as I could tell.   It however was not as pliable as the newer one I replaced it with.  The reason I replaced it is that I was adding a long shaft unit & decided while I had the lower unit off, that I has just as well replace the water pump impeller at that time also.  However any impeller could be ruined after only a few seconds of running without water (been there-done that).

 

A few years ago, I purchased a 70 hp Johnson from a private individual, when I was looking at it prior to the purchase, I asked if it ran, he immediately reached over, twisted the ignition key & started it, (it was still on his boat & trailer).  THE MOTOR WAS NOT HOOKED UP TO WATER MUFFS.  I quickly told him to shut it off, his reply was, that's OK, I ran it like this yesterday.  I immediately looked under the hood for evidence of overheating (which there was none) but deducted $100 off my offer.  And YES the impeller was totally demolished, having the tips of the vanes worn off enough so that it would have pumped very little water. 

Proper Repairs ?? : There are at least 2 ways to repair anything, with outboard motors not excluded.  You can skimp by & just repair or replace what is needed to keep it running & there may be a place for this type of repair.  Or you can go one step farther & clean up plugged water passages, or replace any other parts you find that are not really up to par.  This extra could be a frayed starter rope, a hardened fuel line primer pump, twist grip throttle gears that jump out of mesh, or a leaking gearcase drain plug seal.   I for one do not like the idea of fighting my motors just to get me to, or more importantly, getting me back from the fishing area.  This can also cut deeply into your limited fishing time.  It is a lonely feeling to be dead in the water, and paddling against the tide or wind is not a very rewarding situation, it may however become exciting.

Most parts for these motors are still available from different sources, either new or used, however price may be prohibitive on some cases.  With this in mind you may consider making or repairing your own, or purchasing replacement bolts from the hardware store.   Now I am not saying to tie the broken twist grip handle on with bailing twine, but I am sure human ingenuity can prevail if the need arises.

The mechanical repairs are a usually no brainer, but electrical problems can well be aggravating until you get them figured out.  And since you & I do not normally have lots of new or even used parts that are known to be good, it is hard for us to simply swap out parts until we find what is wrong.  One internet parts supplier includes a sheet listed below with their shipped parts.
 

"---WARNING --- The outboard marine ignition system is one of the more comprehensive electrical designs in the market today.  The most common error made by the mechanic or the owner is to simply replace a defective component within the system without determining what exactly caused it to fail.  "Did a shorted rectifier cause this problem?" or "Did the owner charge his battery improperly?" ; are just a few questions that reflect a couple of the many possibilities for failure.

  Make sure your part is defective for the right reasons.  Always consult your maintenance manual to see that the part you are replacing is the problem and not the result of the problem.  If this is not done, failure will only happen over and over again."

Spare Parts Availability :  Most marine repair shops even though they may not be a OMC dealer, can get parts if they want to.   However a big Honda or Yamaha dealer may not be interested in helping you in the least, where a smaller independent mechanic may.  Also, you can go to any CarQuest automotive store & request a "Sierra" marine parts catalog.   NAPA  also has a "Marine Catalog", which by the way, uses the same parts numbers as the Sierra catalog.  These catalogs will not have all the specialized individual parts like motor mounts or decals, but they do list pistons, rings, bearings, gaskets, seals, water pumps, fuel pumps, impellers, & many ignition parts.  They also will not have current production parts within the last 5-10 years, making you go to the marine dealer. 

 

The one thing about it however, you may need the manufacturers parts manual to give you some of the original part numbers, to properly identify the needed part.   But also bear in mind that even OMC changes /updates part numbers.  This means that the number you get out of a 1983 OMC parts book, if it is still available, may be changed to a totally different part number.  So the dealer can not just order the numbers you give them, they have to look it up in the current parts/price update list to get current part numbers if applicable.

 

Since about 2003 prices for replacement parts for these old motors from Bombardier has raised many times.   It seems when they are getting low on these old parts the prices just keep going UP if they have no intention of reproducing them.  Some of the normal parts are rather expensive, like the mounting clampscrew assembly & the upper motor mounts.  Therefore used prices have begin to climb even on e-Bay.  

 

Bombardier Recreational Products Inc. now has a online parts listing for both the Johnson & Evinrude at http://epc.brp.com/default.aspx?brands=ej&lang=E&dealerlocator=no.  This has a complete listing of parts, with printing off the illustrations possible.   It also has a pick list, that you can print off.  However I have not found any prices, so this must be just that you have the part number information when you go to your dealer.  This will prove to be very helpful in allowing you to decide what parts you need for your motor.   One word of caution, in my effort to research the inner exhaust tubes for the 9.9/15hp, it appears that the actual illustrated parts are not necessarily the exact picture.  The part number is correct I am sure, but the picture may be misleading.

Some Shops Refuse to Work on Old Motors :  There may come the time when you do need to take it to a marine mechanic, because you simply do not have enough spare parts to exchange in testing, or the needed electronic test equipment to diagnose a ignition/electrical failure.  A few years ago I ran into a independent marine dealer who has decided they will not work on any motor over 20 years old, this 9.9 OMC included.  Their explanation was that parts for many of these older motors are not obtainable.  I had what I thought was an electronic problem & in the year 2002, I took my motor in & presented this dealer a complete list that contained the motor year, model, serial number & all the previous repairs & the things that I had done to the motor, like compression test, spark jump test, how it was acting etc.  Now, their refusal may be understandable in one sense, but for this particular series motor that had not really changed that much during a time span of 18 years, with the last of this series being made in 1992, and with parts still available from Bombardier, it seems like they are not really interested in giving service.   And I for one will seriously consider whether I need to patronize them again, unless it is an emergency on my part.   Recently I have heard of another shop doing the same.  My suspicion is these shops are not run by the owners, that their mechanics are of the younger generation & have not been trained on these older motors.   And they think the older motors are only good for anchors.

 

I recently talked to another motor owner, but this time a late 9.9hp Mariner 4 stroke that was equipped with a Yamaha powerhead.  This would have been common in that Mercury used the Yamaha powerhead on their 9.9s up until recently.  This same above dealer refused to even offer any advise as to a choke solenoid problem & even told the owner to never bring it in or even bother him with this JAP import again.   Now this is odd in that this dealer is still a Mercury sales & repair dealer.
 

It seems that we here in the US are spoiled by being able to at least find a marine repair shop within a reasonable driving distance.   In other parts of the world, they are non-existent & if you do find one, the word is that service is lacking possibly because of lack of parts availability, or that they do not see as many as we do here & knowledge is lacking.  In my previous business I made it a point to not charge my customers for my learning experiences.  I just heard from a friend in Germany where mechanic labor equates to $125 per 15 minutes.
 

Since I have had these articles posted on the internet, you would be amazed at the pleas for help that I get from all over the world.  Most of these requests for information are covered in my articles, just written a little different format than the question.   Or they did not read the whole article.  There is a lot covered here & needless to say may need to be re-read numerous times to digest something that the average person may not be familiar with to start with.

Story #1 --   I had acquired a used 1974 "rebuilt" powerhead off eBay that was supposed to have run hot after a recent rebuild.  The owner got exasperated, stripped the motor down & sold the individual parts.

When I got it, & since it was just a powerhead & readily accessible, I wanted to find out any potential problems before I put it on an ailing motor that I had acquired earlier.  Upon disassembly, I discovered that YES, it had seen a wrench before.  Namely a different (red) gasket sealer material under the head gasket, powerhead to upper housing unit & also under the water jacket, indicating that someone had at least had it somewhat apart & looked at it in the not to distant past.  I did also find evidence of the same gasket sealer in between the front & rear sections of the block, so at least the block had been apart & possibly there were new rings put in.  OH yes, and it had a recent gray paint job.

The head & head gasket came off the block OK, but the head gasket was still stuck to the head.  The previous mechanic had not removed the gasket off the head in an apparent attempt to do a cheap overhaul by using the old gaskets.  The suspicion on my part was that this was probably because they were afraid if they tried to take it off the head, that they would ruin it & could not use it over again.  There was however new sealer material between the gasket & the block.

What I did find, was that  the motor apparently had been in salt water numerous times & had not been flushed well.  When I took the gasket off the head, there were salt crystals/aluminum corrosion pretty well blocking the lower cylinder's water jacket passage in the head.  This model has the thermostat at this lower location.  The water passages were blocked solidly enough that I doubt that very little water could have even passed on into the plugged thermostat, much less on thru the rest of the engine & on out.  Pictures are shown below in "The Possible Water Circulation Problems" section below.
 
Story #2 --  Another situation presented itself that bothers me, relates to dealer ethics.   I again purchased off eBay a 1987 15hp Johnson motor for $76 that was sold as "needing repair/for parts".  It was close enough (150 miles) that I drove & personally picked it up from the young man.  He advertised it as needing rings & that he had the marine shop's estimates.  He is a young Coast Guardsman & had gotten the motor from his father 2 years before.  On his first attempt ever to start it this spring 2005, it would not start, so he took it to a marine repair shop in a decent sized town located on salt water with lots of boat traffic, which should have had enough exposure to be pretty well acquainted with outboard motor problems, plus they did all the Coast Guard's repair work.  He had also broken the starter rope in his efforts, since he apparently was not aware that the motor needed to be in neutral when trying to start it.  The work order he gave me from the dealer says "low compression - pull head & diagnose, & call with estimate.  recoil repair".

The diagnosis reads "Bad Rings - new power head, not cost effective to repair unit".  They had taken the head off, inspected the piston & rings,  re-bolted the head back on lightly & without the gasket (apparently to prove they had it apart).   The headgasket, broken recoil starter rope & handle were stuffed under the motor's cowling.  The estimate of needed parts included carburetor kit, fuel kit, water pump kit, rings, rod bearings, wrist pin & bearings, main bearings & seals, oversize pistons & rebore to match pistons & a thermostat for a total parts estimate of $294.  This mind you did not include the labor.

OK, on the surface this looks like it could be appropriate.  But after I got it home, I noticed on the top of the flywheel was written in felt pen, "Comp 1 -  100#,  2 - 105#, & spark OK".  I took the head back off & the pistons were clean, with no carbon, there was wear of about .010 in the cylinder walls but very little piston wear.  Yes, it was WORN a lot as the pistons could be wobbled.  But my thoughts were if compression was at the 100#,  why did they even take the head off?   I just reassembled it using the original head gasket with some gasket sealant.  I had a used starter rope that I installed.  BUT -- the one thing I did install that was missing, was the "C" shaped horseshoe clip in the kill button on the end of the twist grip.

I had the motor running within 3 min.  My question is, how did they check the spark without using their own clip on the kill button.  And with the broken starter rope, they would have to have used a emergency starter rope, not an impossible thing.  It would appear that they never told the young man about the "kill override switch, otherwise known as man overboard switch" was missing.  OK, maybe this now running motor is not 100% factory new, but I will bet that it will run for quite some time as a normal fishing motor. 

  

My guess is that this young man did not know anything about the "Man Overboard Kill Switch Lanyard" that was missing.  With this gone, it was essentially like turning off the key.  They could have replaced the starter rope, changed plugs, adjusted the carburetor idle & charged him $75-$90, he would have been happy & they made a enough to cover the diagnosis & the actual repair to have made a profit.  I will bet they even tried to sell him a newer motor & or offered him a minimal trade in.

Story #3 -- I happened to be talking to my neighbor & school mate when I spied an older 10hp QD Johnson, I asked how it was running.  His response was, well it had belonged to his Dad many years before & had been setting for some time, & when his sons decided to use it, sad to say the water pump did not function.  They took it to an independent mechanic (well known to the locals as being a scalper), who replaced the water pump for a mere $200.  They thought they got a good deal, as he told them that a new motor of that size would have cost them over $2000.  This may not have been a proper comparison, but in any event the repair was still about 1/2 of the price of a used motor of the same year.  This mechanic probably had an hour labor & possibly $20 worth of parts in this repair.  From the experiences I have had with this mechanic, he is one of those smart A$$es, looks at how you dress, the vehicle you drive, plays a sucker game & adjusts the price accordingly.

Just one more of the reasons why I am writing this article.

History :  Johnson was one division of OMC, (Outboard Motor Corp) while Evinrude was the other.  This came about by the merger of both companies in the early 1956.  Both brands of motors came from the came plant after that.  Evinrude was usually painted a blue color of some sorts, while Johnson was initially green until 1977 & then white.  Late 1990's they both were black.   OMC filed for chapter 11 bankruptcy &  in October 2001, & Bombardier Corp. a Canadian manufacturer bought the outboard motor division.

The earlier 10 hp QD series motors were made from 1949 thru 1963.  If you need year of  a manufacture for these motors, or any before OMC went to the year code, as described below, go to http://www.marineengine.com/manuals/johnson/.

 

 

The  9.5 hp, was built from 1964 to 1973, which was a the first of the low profile motor series, and  is not a sleek looking motor in my opinion, with a squatty oversized motor cover & upper housing sitting on a standard lower unit.  The lower unit was not unitized like the later 9.9's, in that the bottom half of the 9.5's at the output shaft was split (like the QD' series) although allowing easier access to the shaft & gears.  I understand it was also basically a souped up 7.5 hp motor.  Some experienced mechanics say the crankshaft did not stand up under heavy usage as a 9.5.   It apparently was not designed for remote controls, therefore the one shown below may be an aftermarket kit.

For those of you who have asked, the water pump impeller is the same for these 9.5 motors as the previous 10 hp from 1958 - 1963 but not the same as the 9.9s.

The 9.9 hp motors covered in this article, came into being in 1974.   As for actual physical differences between the 9.9 & the 15 hp that you could use for identification other than the decal markings, year by year these 2 hp sizes & brands are the same.  If the top cowling was removed & lost, the name/model plate was missing, then to tell the difference you may have to remove the carburetor & measure the inside throat to tell if it was a 9.9 or 15 hp. 

The Johnson line of 9.9 motors remained the same as far as calling it a 9.9 hp.   However Evinrude had a 10 hp designation on some of the later ones from about 1990 or so.   Same motor, but they just changed the stated rating for advertising purposes.  The reason this motor was called a 9.9 hp, was at the time of it's inception, the Coast Guard's terminology for registering a boat was that if it used a motor of less than a 10 hp & the boat was less than 16' long, it did not need to be licensed.  This classification has now been changed.

The piston diameter for both the 9.9 & 15 hp motors are 2.188" with a stroke length of 1.760"  which equals 13.2 ci   or 216 cc.  Full power operating RPM for the 9.9 is 4500 - 5500.  The 15 hp motor is rated at 5500 -7000 RPM according to a 1978 Johnson sales brochure.
 
These were the second series of motors in this size range which were made with the compact lowered powerhead (the 9.5 being the first) & more easily fished over the top of & set the trend for other manufacturers to follow.  This series of motors appears to have been among the first of the thru the prop exhaust motors.  The outward appearance of this motor, other than paint & decals, remained virtually unchanged for 18 years, & even today (2006), it evolved into the backbone for the current 2 stroke model.  Both the current 2 stroke & 4 stroke motors use the same water pump & virtually the same lower unit (slight external changes) as the 1974 version.  OMC apparently learned something on the 9.5, as the 9.9 is basically a detuned 15 hp, initially using only a different carburetor & decals on the cowling. 

Observance :  When a new design is brought out, it seems that there will surely be modifications needed to correct unforeseen defects or problems that do pop up.   However it seems when OMC came out with a new design or an "improvement" to the design that they are hesitant in making a quick change for 3 years.  This is evident in that the first models in 1974 used points & coils until 1976 when the electronics went to a Capacitor Discharge system.  The carburetor seem to be changed in either 3 or 6 year increments.   When the later motors came out in 1993 the plastic lower cowlings ran for 3 years even though the plastic top cowling latch was prone to breakage.   Then the 1997 was a revert back to an improved version of the earlier cowling rotating lever latch as previously used.

It is suspected that possibly they want the design to run for long enough to really perfect a better part?   Or more than likely that they needed to keep those parts in production so that inventory restocking would not become a nightmare by being changed every year or so.   If they worked on a 3 year cycle it would not be as bad & a better parts interchange.                                                                 

 

Year of Manufacture :  This is important in any repair, for obvious reasons.  Prior to 1979, Johnson used the last 2 digits of the year in the model number.  As a model 10R78M, would indicate a 10 hp, Rope starter, 1978 year of manufacture & M model revision.  Since this does not have in the code L between the hp designation & the year, it is a short shaft version.   Evinrude in those years used a different 5 digit model code, as 10424.  The numbers  you are looking for will be the first 3 numbers which equates to the hp & then the middle to the year, as 10 hp, the (4) equates to 1974.  Here is a LINK to help you determine any of the Johnsons.  And here is the LINK for the Evinrudes.

 

After 1979, OMC's manufacturing year code, which included Evinrude, is the word "INTRODUCES", with each letter equating to a number ie:  I=1, N=2, T=3, R=4, etc. as illustrated below.  As before, the last 3 letters are what you are looking for.  Then in this case, disregard the last one, as it pertains only to a model revision that only on specific cases may be revalent to a marine repairman if problems arise.  A code of  J10ELENA would equate to Johnson, 10hp, Electric start, Long 20" shaft, EN = 1992, & the A could be a model revision, so this motor would probably be made in the very first part of the year.  You may encounter a code of something similar to J10SELCTC. This would have been  Johnson, 10hp, SailMaster, Electric start, Extra Long shaft, 1983, & the C could be a model revision.  In this case with the SE in the model number, indicating a SailMaster, all the SailMasters would have all had the extra long 25" shaft.   For more detailed information on worldwide production, CLICK HERE

 

 

Using this code system, if the motor was sold as an Evinrude, then the first letter would have been an E instead of the J.   Then you can encounter motors made in or for other countries, which will have some added letters as mentioned later in this article.

Sometimes  the nameplate found on the LH side of the upper steering/clamping bracket can get removed.  If this happens, you can still usually tell which motor it is by looking at the 25 cent size soft plug in the upper rear RH side of the block.  The model & year are stamped in this soft plug also but probably only up to 1979.  It is interesting to also note that the 15 hp uses the same block as the 9.9, so you could see a 15 hp with the same 10R78M numbers here as the 9.9 has.   I have heard from one person that his plug had numbers that do not match any of the codes, so this kind of backs up the idea of a change after the 1979 date, as the factory changed things as time went on.

In 1981 the marine industry went from powerhead rating to a prop rating.  The word was that the imported Japanese engines of the same rating were outperforming the US engines, as they were rated differently.  To get the equivalent prop HP on a US motor prior to 1981, take the HP rating & subtract about 10%, this will get you close to the newer rating.

 

One thing that I have found is that the motors which have the points & condensers (1974-1976) seem to be a little cold blooded, in that they have to warm up before they will stay idling as for trolling.

 
Controls from 1974 to 1985:   This series of motors have all the same basic controls.  That is on the front panel, the choke pull knob is on the left side looking back to the motor.  To the immediate right is a large (approx 1" dia) knob that rotates, but will only go about 1 turn.  This is the carburetor idle adjustment knob.  In the center is the manual starter pull handle.  On the far right will be the kill button.  If it is electric start, on the left side, hidden in the mounting base is the start button.
 

On the left side looking forward, is another large black knob located immediately behind the fuel line connector.  It is the idle speed control screw.  In effect this is basically for setting a trolling speed, where you want to return to after making a run without playing with the twist knob.  In setting this one, you may have to adjust it & the carburetor idle knob simultaneously to fine tune each.  This idle speed control knob is prone to abuse & the snap ring retainer groove can get broken which allows this knob & stop screw to become inoperable.  It is unique in that the threads are LH.  

One cure for it without purchasing a new knob is to do some measuring & eliminate the wafer washer under the snap ring.  Put the knob in a metal lathe & carefully move the shank back into the knob area, deducting the .050 of the washer & recut the snap ring grove.  Shown below is some dimensions.  The purple lines are what was removed.

 

 

On the right side again looking forward is the shift lever.  These shifting levers will be evident in the pictures listed under "Ignition".  Below the shift lever but just above the mounting brackets is a lever that moves forward & back.   It locks the motor down so that if you put it in reverse & try to attain a high speed, that the lower unit will not jump up & out of the water.  This lever, when moved forward, allows you to raise the motor & lock it in the up/out of the water position.  Also in the same 2 bottom pictures referred to above, you will see the black lever described just previously. The upper cowling lever is located at the rear & under the edge of the cowling, rotating it down allows you to remove the upper cowling to access the engine compartment.

 

Controls from 1986 to 1992:   In 1986 a change was made to the tiller handle/throttle twist grip, I call this the type 2.   A cable system replaced the gear throttle linkage greatly improving the situation dramatically.   At this time they also moved the kill button to the tiller handle & added the lanyard type kill button on the end of the twist throttle handle.  This created a problem if you used the extended universal joint tiller handle, as you could not reach the kill button with this extended handle installed.  

 

Three or four years later the handle was changed slightly & the kill button was moved to about mid handle left side.    These buttons also incorporated a man overboard kill switch.  The motor comes with a red coiled plastic cord that is attached to a split plastic section that is inserted UNDER this button.  The other end of the cord is to be attached to the operators wrist, so that in the event he falls overboard, this insert is pulled out & the red button goes deeper in the housing & the connection is disconnected, just like turning a switch off.   In use this red button HAS to have either the lanyard insert under the button, (turning the ignition ON) or a another smaller that one called a "restart clip" shown below on the 2 photos on the right, that is inserted instead of the lanyard if the owner decides he does not want the lanyard safety device.

 

On type 2 & 3 the end plug is made to rotate.  This is to fine tune adjust the idle for trolling, as these motors do not have the LH side trolling adjustment knob.

 

 

The type 1 twist grip may have different grips depending on the vintage of the motor, the early ones being a white plastic.
 

The electric starter button remains in the same position on the LH side in the mount clamping area for these motors as the previous versions.

 

How to Start Your Motor :  The first series in 1974 had a nameplate riveted onto the bracket just below the control panel, stating:

 "Starting Instructions:  Read owners manual.  Connect fuel line to motor.  Squeeze primer bulb unit pressure is felt.  Shift to neutral.  Twist grip to start position.  Pull choke knob out.  Pull starter handle.  Push in choke knob as engine warms up.  Stop button on control panel.  Spark plug UL4J.  OMC  sea-lube gearcase lubricant."

Engine Has Sat For a While :  If the engine hasn't been used in quite awhile, very possibly with gas sitting in the carburetor, it may possibly require cleaning, which seems to be the standard recommendation for motors in this situation.  However, it may be worthwhile to try to run it at least once before jumping into a carburetor repair.  I have found that sometimes the gasket between the main carburetor body & the bottom fuel bowl can deteriorate.  When this happens, for what ever reason, chunks of the neoprene gasket get into the fuel bowl & can partially plug the high speed jet, cause erratic engine performance.  It has also been found that the newer non-leaded gasoline is less likely to cause internal gumming problems in the carburetor if allowed to set for extended periods of time.

The only way to fix a clogged/fouled carburetor is to remove, dismantle, clean, and rebuild it.  Do not try to spray a carburetor cleaner in the breather or run it thru the fuel & expect it to do a cleaning job.  If you try this while the engine is running it very well could ruin the engine, as there would be little lubricant inside the engine for the bearings.  If you take the carburetor apart, make notes and drawings as to what goes where, or use a digital camera.  Regardless of how simple it seems, you will find something where you can't remember how it should be when it comes time to put the parts back together.

 

The One Weak Thing on This Motor :  The first series (that I designate as type 1) up to & including 1985 uses twist grip gear teeth to activate the throttle on this series.  As described above these gear teeth  mesh on both the twist shaft & the mating  linkage shaft gear function so that the handle can be raised & lowered & yet be twisted.  BUT this feature was not really intended to be used this way as mentioned earlier under "Remote Controls".   DO NOT RAISE the handle very high & twist the throttle unless you are prepared to disengage the gears, & change the twist grip timing relationship.  This is explained in a subsequent section.  Pictures show this relationship in the Trouble Shooting section.   Later, in about 1986 a throttle cable push/pull system was used to eliminate this problem.

 

Difference between the 9.9 & 15hp : When they designed this series of motors, they designed it as a 15 hp & then detuned it with a different carburetor for the 9.9.   When the 9.9hp and 15hp came into being in 1974 and up thru 1978, the only real difference between the two motors was the carburetor.  In 1979 they added a shim, part #325038, (one for each cylinder), behind the leaf valves & under the stop plate for the 15 hp, apparently to allow the motor to suck more fuel & air mixture in.  

 

The outside visual dimensions of both carburetors appear the same, unless you look inside the throat.  If you look in from the rear, you will have to position the throttle plate to a horizontal position to be able to see the throat very well.   The 9.9 hp carburetor’s internal throat is .625 dia., 15 hp internal throat is .875 dia. up until late 1987 when they went to a plastic topped carburetor.  The outlet or rear throat dia. is the same on both to match the manifold port dia.   The idle jet venturi system is also slightly different between the two.  The part number for the the pre 1987  9.9 hp Carburetor Assembly  is #388936, while the 15 hp Carburetor Assembly is #338273.   This increased throat dia. & larger main jet allowed it to breather better & pull more fuel in, increasing the RPM about 1000 RPM.  

 

 

A problem in buying a used carburetor is that the part number may be hard to read as it is only stenciled on.   And many people, even marine mechanics, do not see enough of these to be really sure which is which unless they see them side by side.   The reason for this is that when these motors were sold new, say in 1978 the 9.9 went for $595, while the 15hp was another $150.  Needless to say way more 9.9's were sold than the 15's by possibly 80%, therefore considerably less used 15's parts are available.

 

In 1981 there was a change made in the inner exhaust housing for the 15 hp OMCs only.  It was a sort of tuned round exhaust housing, allowing the engine to again breathe better, which  in addition to the larger throated carburetor, & the leaf valve shim gained about another 10%  in overall HP to put these OMC engines on par with the Japanese imports.  The 9.9  square inner exhaust housing & no shim for the leaf valve, stayed the same as it was.  The big difference in the performance between the 9.9 & 15  hp will be in the last 1/3 of the throttle range where the increased fuel/air flow of the carburetor will be readily apparent with the increase in RPM.  

 

In the photos below, the 9.9 exhaust housings are on the left with the 15 hp on the right in both photos.

 

Later motors, at least a 1992 9.9hp uses the 15hp exhaust housing.  
 

You will note that there were 3 different ongoing 15 hp modifications.   (1) The 15 hp from 1974 to early 1987, with just the different carburetor.  (2) The added leaf valve shim in 1979.  (3) And the added tuned exhaust system in  1981, which also included the 2 previous modifications.  The 1979 parts manual lists a shim, part #325038 to go between the leaf valve & the stop for the 15 hp only.  This shim sells for $2.94 each.  It is carried on up into 1992 for the 15 hp, which apparently allows the 15 hp to breathe a little better.   These leaf valves are the same for all motors they are used on.

 

Carburetor, early :  Do not think that you can up the horsepower by simply modifying a existing 9.9 carburetor by replacing the main jet with a 15hp main jet.   All you accomplish is that the engine is being fed too much fuel & not enough air to properly mix with it & the engine will then blubber (floods out) at the top end.   It can run OK on the lower end & idle OK because it is using the idle jet then, but it will have less top end power than with the original 9.9 main-jet.   Believe me, as I have been there/done that.  Matter of fact that is what got me into writing this article, as I could not readily find any factual information on the subject.  To reiterate the above, a 15 hp main jet modified 9.9 carburetor WILL NOT work.

Factory specification rating for RPM of  the 9.9hp is at 5000 & the 15hp at 5500.  With operating range for the 9.9hp at 4500 to 5500 RPM, & the 15hp at 5500 to 6500 RPM.

If the float bowl gasket on the carburetor is black, it is the older cork material used for bowl gaskets, & the float will usually be cork also, then you are probably way overdue for a overhaul.  There could be pieces of this cork gasket floating around inside the bowl, occasionally plugging the main jet.

Early production motors had all metal carburetors. Then from about 1980 to late 1987 the same basic carburetor as previously was used, but had a black plastic bottom fuel bowl.   This seemed to be an improvement if water had entered in the system & got in the bowel, then sat for a while creating RUST inside the carburetor & even enough rust on the outside if used near saltwater to corrode holes in it.  If you have to replace the metal bowel the cost is $24.00 as of 2005.   I have however seen metal bowls on 1982 to 1985's, but not sure if the carb. was ever changed or not. 

 

Carburetor, late : Late 1987 & newer production carburetors up thru 1996 were completely different & had the bottom fuel bowl & top made of heavy black plastic.  They were apparently designed for easier manufacture as the plastic top has the idle jet in it & the juncture between this top & the main body serves as a passage (depending on the the gasket) for the fuel from one chamber to the other.  There is a white nylon collection box that is sandwiched & gasketed between the main body & the bottom fuel bowl that has a removable main-jet on one side.  These carburetors appear the same for the 9.9 & the 15 hp with the exception of the main-jet AND the throat dia. in the main body.  In the parts list, the main-jet for the 9.9 is spec'ed out at a hole #34 (.055dia), while the 15 is #54 (.110  dia.).  The idle jet suction tube comes off this collection box & goes up into the plastic top for suction to the idle jet itself.  This arrangement appears to help keep debris out of the jets.  

 

The choke butterfly is the same as the previous models, but the throttle plate is smaller.  The internal throat of the 9.9 is about .500 dia. while the outlet hole into the manifold is .750 dia.   This is quite a bit smaller than the earlier versions, & the guess is that this newer carburetor is probably more efficient.  It appears to have all the screw holes & outboard fittings in the same locations, but whether it would interchange with the earlier versions & function reliably is a question.  Probably not in that the the internal castings of the intake manifold  appears different also. OMC repair kit  #439073, or NAPA /SIERRA part# 18-7219.

 

If it is more efficient,  then the motor will possibly idle better & have less of a black oily residue ooze out of the lower part of the exhaust housing for weeks after it is put into storage.  One other observation while the carburetor is off, you will notice the intake manifold has a slight vertical separator on the bottom section up about 3/16".  The supposition is that this may help fuel flow to the individual cylinders better.   These later carburetors also had an adjustment screw for the cam follower.  

 

Both these older & newer style carburetors use the same air box or silencer, but to most of us it is known as the air breather.

 

If you see a carburetor advertised that does not have the above RH side choke lever, but only a shaft protruding with a roll pin installed, it will be for a 1993 or later motor, as the choke lever is different.

 

Update Carburetor :  The original carburetors used on the 1988 -1993  9.9 HP  had a plastic cover which didn't have a sufficient number or retaining screws that let the cover flex on acceleration and could cause stalling or stumbling and poor idle.  The new carburetor, part # 436779 is a factory update carburetor which replaced these defective plastic bodied carburetors.   Dealer cost was $244.42   It is not known whether this was a factory recall on this, but probably just if you brought it in & complained.  Now that OMC has sold it surely is not honored anymore.

 

Removal of the Carburetor :  You need to remove the plastic carburetor intake cover (OMC calls it a silencer).   However the early ones I have seen are white instead of the common black color that is on the later versions.  It just could have been that some  motors that had white ones that were made of a material that did not survive vibrations as I have seen may missing.  Remove the choke lever & the idle knob.  When removing the idle knob, make note as to the location where the indicator tit is pointing, as you should replace it in the same location when reassembling.

 

You also need to remove the recoil starter unit. The manual starter unit can be unbolted with the one 9/16” headed bolt head in the center of the recoil unit.  Be very careful as that spring is dangerous! Pull the rope out a few feet and tie a slip knot in it so that it can't rewind back.  Carefully remove the starter handle, then grab the rope inside at the starter pulley, then let the rope withdraw somewhat but not completely (leave a foot or so to work with).  Now, secure the rope inside at the starter pulley to the upright pulley gear guide in a manner that will prevent the spring from rewinding the cord etc.  Hold the manual starter assembly together when loosening the top large retaining bolt (do not remove that bolt completely from the starter housing assembly).  Carefully remove the starter assembly while holding it together.  Screw a 3/8" nut on the bottom of that large retaining bolt to hold the starter together while you're working on other components.   

 

There is a small coil spring (#1 in the photo below) from the carburetor to the ratchet of the starter & up to about 1979 that needs to be unhooked.  This spring's tension is released by a lug that the timing plate cam positions when the twist grip & shifting lever are in neutral.  If the throttle is faster & the motor is in gear this black plastic dog drops down into the starter spool teeth, not allowing the manual starter to be pulled.   This dog's function will still operate by gravity if the spring #320490 is missing, but not as positively.  This spring is obsolete & only available from aftermarket suppliers at a cost of $9.95.

 

There is also a Z link rod (#2 below) This ties the roller bar unit to the throttle valve of the carburetor.  Do not loose it either, or a makeshift one will need to be fashioned as this #2 is below from a piece of welding rod.  The important thing here is to get the bends just right so that the timing is consistent  when the timing plate moves this roller forward to give movement in the throttle valve increasing fuel flow.
  

 

Now you can get to the RH (looking forward) carburetor nut more easily.  The LH nut is harder to get to & you may only get the nut to move one flat at a time with the wrench.  You may also decide that by removing the flywheel it is easier to get to this LH nut.

 

Remove the fuel line. 

 

Clean & Rebuild the Carburetor :  Disassemble the unit.  Once the carburetor is off, unscrew the bottom screws that hold the sheet-metal bottom pan on.  When removing this pan, be careful & try to save the gasket if you are not going to get a repair kit.  Remove the cross pin that holds the float, remove the float & the needle valve.  You will need to also remove the idle shaft screw, count the revolutions it takes before it comes out.  In this way you can replace it with the same number of revolutions when you reassemble it.  If the insides are dirty, you can get a can of carburetor cleaner & spray on or soak until things soften up.  Usually you can use an air hose to blow thru the passages & be sure they are clear.

 

There is one solution that works great to soak carburetors in, it is any of the outboard de-carbonizing liquids.  One that is universally available at even automotive supply stores is Sea Foam  http://www.seafoamsales.com/ that is used as a fuel additive to help unstick hydraulic lifters or run it in the gas to decarbonize piston rings.  It will not damage any of the rubber parts.  Just soak it overnight.

 

You can possibly get by without a repair kit or gaskets if you are careful in your disassembly do not use a gasket sealer when you reassemble it as some may dry out when the motor is stored over the winter & some of this sealer may dry out & chuncks of it can get in the main-jet.  Later gaskets were a neoprene type positively does not need any sealer.  If it just had debris & water in the bottom, you can get by without a repair kit.  But if it is gummed up varnish you will need to go farther.  Check the idle needle valve for straightness of the tip, if it got dropped, this tip can get bent.  If you are good, you can possibly straighten a bent one, otherwise just get a repair kit.

 

For the price of a $12.75 repair kit for the early versions, while about $21.75 for the later style.   You get all new gaskets, needle valve, main jet & new metal plugs that are needed to replace the old ones if you have to get all the channels cleaned out, and float adjustment instructions.

 

The older floats are made of varnished cork & can get deteriorated over time & may not function properly, if so replace it with the newer black plastic type.

 

When reassembling, place the float back in position & replace the cross pin.  Tip the unit upside down & check the float height.  The now upside down unit should have the top of the float parallel with the now top of the housing.  If not, you can adjust it by bending the metal tab that acts as a stop for the float.  Be sure that the float can move up & down freely, otherwise if it binds, the motor may run at different speeds depending on how much your boat is tipped to one side or the other.

 

Screw the bottom pan back together & reinstall the carburetor onto the motor's intake manifold.  Remember to reattach the small spring on the starter ratchet if it was made prior to about 1982.

 

When reassembling the idle jet screw, & you forgot how many turns it was set at, a good starting spot would be to screw it in until it lightly bottoms out, then back it out one & a half turns.  After you get it running & slowly lower the speed, try to turn this screw either in for out for a better blend of air to fuel mixture at an idle.

 

Removal of  intake manifold :   It is very unlikely that you need to do this, but just in case here are some pointers.  It is just about as easy to remove the powerhead from the midsection as try to just remove the manifold.  The bottom 1/4" bolts are a tight location to access.  While the carburetor is off, you will need a 1/4" drive speed handle & preferably a 7/16" wobbly socket, (one that is a combo universal joint & socket combined). You may be able to squeak by with a universal & a thin socket after taking out the front motor mount screw, which will allow you to gain a slight amount of room.  The hard ones are the RH & LH bottom, as the RH bolt is tucked under the support bracket.  The LH one you will have to remove the bolts from the shifter shaft & slide it to the left enough to get the socket on the bolt head.  On motors made in the first 2-3 years of this model, I have found that these bolts are indeed a 1/4" course thread, but using a  head size of 3/8"

 

You may be able to twist the manifold enough to get it up & out from under the throttle cam plate.  But in reassembling when you have the gasket in place, it may well be best to remove the stator & timing plate.  In doing this you now can position the manifold & gasket in the proper place without disturbing the gaskets location.  Otherwise you may be taking it off again, as there is a fuel drain hole in the bottom of the manifold that allows excess fuel to drain back into the crankcase, that if not sealed good with the gasket, will allow gasoline to dribble out & down along side the block & upper housing.  

 

Check the leaf valves, (commonly called reed valves) or replace them.  Clean the old gasket & use a good gasoline resistant sealant on the new gaskets & reassemble in reverse order.   Be sure if you use new gaskets that you use the right ones, it uses 2 different ones with slightly different small holes on one.   Also be sure that you install these gaskets on the proper sides of the valve plate.  If you get them mixed up, the wrong one has a smaller size opening on at the reed valve area & WILL restrict the valve movement to where the motor will not be getting any fuel into the motor itself.  

 

Reinstall & Adjust the Carburetor :  After reinstalling the carburetor to the intake housing & you need to reinstalled the choke knob.  The choke knob shaft has a slot in the middle that the carburetor's choke lever goes into.  This shaft needs to be installed with the longest length of the slot upwards, otherwise the choke lever does not have enough room to function.  Now you need to re-install the plastic carburetor intake cover.  The idle knob is next.  Even after you replace in the same location as it was before tearing it down, & you get it running again, you may need to fine-tune adjust this idle knob for trolling.

 

There is also a large knob on the left hand side of the lower cowling on all but the very early years motors.  This large knob activates an internal threaded rod that acts as a stop for the throttle plate linkage & is used for a slow speed setting, (not to be confused with the actual carburetor idle settings).  After 1987 this knob was discontinued when the cable throttle system was instituted.  The new slow speed setting was then changed to a twist knob on the end of the twist throttle.

 

After the motor has been run enough to have it warmed up, try to let it idle.  If it runs to fast or slow you can adjust the large knob stop screw on the motors left hand side.  It may be best to initially do this with the motor cover off, so that you get an idea of which way to turn this screw. Turning this knob counter-clockwise pulls the threaded rod out & makes the motor run slower.  

 

When you get the motor running at your trolling speed, then turn the carburetor idle screw knob  (lean/rich) clockwise a slight amount, let the motor run for a few minutes, & rotate it slightly more in the same direction again. Doing this you are making the motor run leaner.  Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting & the smoothest the motor will run at slow speed. 

 

When you have finished the above adjustment, pull the knob off forward & reinstall it so the pointer in the "DOWN" position. You will now have a "GO TO" position if need be, which will be discussed later.

 

It make sense when shutting down the motor for what may well be a extended period of time, to disconnect the fuel line & run the motor unit it dies, using up all the fuel in the carburetor.

 

Hard Starting When Cold :  The one most common problem with hard cold starting, if the motor is in reasonably good running condition, can probably be contributed to someone who uses the motor strictly for lake trolling & is prone to adjust the idle jet lower than it is actually designed for.  When you are adjusting this timing & idle jet for slow trolling, you will be doing so while the motor is warm & running.  Then when the motor cools down, things are going to be slightly different.  What happens then is that in the cold starting mode, the motor does not get enough fuel, & you have to choke it & pull more times on the starter rope to get enough fuel into the cylinders for it to fire.  One thing you may do in this case is to after you have adjusted it for your trolling speed is to then pull the knob straight forward & off the carburetor idle shaft, reposition the idle knob to position the pointer straight down & push it back on.  Then when you go to start it, you twist this knob counterclockwise all the way up (about 90 degrees) till it bumps.  This should give you more fuel to start, & then you can reset it to your known trolling position later.

 

One problem could be leaky reed valves at the reed valve base.  This could allow some of the intake fuel to be pushed back out on a firing cycle.

 

Another possibility is that the engine may have worn/leaking crankshaft seals.  This condition will not allow sufficient vacuum on the intake stroke to pull fuel from & thru the carburetor.  This is usually the top seal that is bad.  It will usually make a mess under the flywheel, namely fuel/oil mix spilling down around the block.

 

Motor Not Revving Up Like it Used To :  If all other normal things have been checked out & the motor will not run at the faster speed, sometimes if it has sat for some time with the fuel not run out of the carburetor when it was put away, the main jet can get partially plugged.  The bowl of the carburetor can also accumulate some debris.  If this happens, the motor may start & run at a medium speed, but is not getting enough fuel to allow it to run at a faster speed. 

 

The other thing is as mentioned previously that the twist throttle gears may be out of mesh.

 

Also if the timing plate linkage may have become disconnected from the upper throttle linkage peg, the motor will not run right.  This peg has a plastic bushing & wavy washer with a small cotter pin holding it all together.

 

Timing :  The throttle cam plate that rotates under the flywheel when you twist the twist grip has an arrow type mark on the front of it.  This mark needs to be timed so that when you advance the throttle twist grip, that the carburetor roller is at this mark when the carburetor throttle shaft just starts to turn open.  To adjust this, you loosen the 2 bolts on the RH side of the plate & adjust the cam plate to where it just aligns with the roller at the same exact time that the throttle plate begins to rotate.

 

The timing mark on the timing plate cam does not need to be at the low end of the twist grip rotation.  On these motors, at low speed, the the timing plate will move counterclockwise AFTER the carburetor cam movement& throttle butterfly valve will stop.  This allows the timing to go where the motor runs at it's slowest before it would die, while not moving the butterfly valve, & if the low speed side of the carburetor, (the carburetor air jet idle screw) is set right.
 

Manual Starter Anchor Bolt Threads Becoming Stripped :  If this happens the threads in the aluminum base plate are what is stripped.  The manual starter will become floppy & may have problems engaging the flywheel ring gear.  If used extensively in this condition, the plastic starter spool gears will get chewed up.  The only practical way to cure this other than replace the manifold, is to drill out the base hole & tap it to install a Heli-Coil insert thread back to the original 3/8" NC thread.

 

Replacing the Manual Starter Rope or Spring :  The easiest way to replace the rope is to take the handle off, let the rope go to release spring tension and remove the recoil starter from the engine.  You can then remove the pulley and replace the rope.  On this recoil starter, the rope pulley is in two pieces held together with screws.   Watch how it comes apart and you should have not problem.   Re-wind the new rope (counter-clock wise) and re-install the starter.   Take a turn or two around the pulley with the rope to tighten up the spring a little and run the rope back out the rope hole and attach the handle.

If you are just replacing the rope, use a little caution when you pull the pulley free of the rewind spring.   They stick sometimes and can pull the spring out.   You don't want the spring to come out of the lower metal housing, otherwise it is a messy & tedious job rewinding the spring back into the housing.   Which brings us to replacing the spring, take the old one out, but be careful in that if it uncoils from the housing it can be dangerous, like a snake whipping around.  in replacing a new spring, they are encapsulated by a metal clip.   Some of them come with a metal clip retainer holding the spring wound up tightly.  Others the coil will not be wound as tight as needed to be placed inside the cup unit.  If the tight one, you are in luck, place the new spring in the old housing, & then take off the clip.   Rewind the rope & reassemble as described above.

 

If you need to rewind the old spring, or replace the large wound coil.  My experience is best to start it into the cup base with the outer looped end sticking out the slot.  Then wind the spring inside of itself, being very careful to hold things tight as you wind each successive coil inside the others.  Once you get the whole spring encapsulated, you can take a brief breath.  Now you can wind the rope back onto the spool & locate the spool's inner peg into the eye of the spring.

 

 

Reinstalling the Manual Starter Spool :  New rope is 5/32" dia & 72" long. The spool has to be replaced in the proper location.  The underside of this spool housing has a 90 degree metal lug protrusion that hangs down & goes into a round hole in the base that the unit bolts onto.  It is hard to see where this protrusion goes unless you place a felt pencil mark on the housing in line with this metal protrusion.  There is a flat washer between the mounting housing & the starter spool & under the recoil spring.  Be sure this washer is in this position, if you put it below the housing & above the bracket, the housing will compress the unit to the point it will bind & the spool will not rewind freely. 

 

The manual starter spool assembly was changed after 1978.  The rewind spring was changed in that the inner end of the early springs had a sharp bend back end to attach to the spool, which proved a weak point & would break.   In 1979 & later they added a separate starter spring retainer which linked between the spring & the spool.  At the same time the neutral safety interlock system & ratchet teeth were moved from the top to the side of the spool.    

 

You need to have the anchor bolt backed almost all the way out of the housing (but not all the way, otherwise the coiled spring may pop out of its housing) when you place the unit in position.  If when you get the spool unit in place & the metal protrusion in the hole, but have problems aligning the bolt into the hole, hold the unit together as best you can & you can remove the bolt.  Now you can look down thru the bolt hole & align the hole in the housing to the threaded hole in the base.  The flat washer needs to be installed under the anchor bolt's head, otherwise the starter gear will not stop on it's upward motion & bind in the flywheel gear teeth.

 

You will find it harder to get the manual starter out & back into position if you are working on an electric start version, as this ring gear makes for a closer fit.                                                                    

 

Removing the Flywheel:  If you have to remove the flywheel, you will first loosen the nut on top with a 7/8”socket wrench.  Unscrew this nut 3 or 4 turns.  There are 3 holes around the center of the flywheel that are designed to use a 3 armed puller.  However if it is not stuck excessively tight, you may be able to remove it by the alternate method.  Holding up on the flywheel, & with a plastic or lead mallet, tap this nut with a sharp rap or two.  This should loosen & pop the flywheel off the tapered crankshaft.  If this doesn't  loosen it, then you will have to use the 3 armed gear puller & the 3 holes in the top of the flywheel like it was designed to do.  Inspect the flywheel key for sloppiness or evidence that it does not fit snuggly, as this can allow the flywheel to move slightly & change the ignition timing.  Note, there is no lock washer under the nut here.

 

 

Ignition :  These motors have transitioned thru 4 electronic ignition systems. The first 3 years from 1974 thru 1976 has a straight magneto setup with points and condensers, but does have external coils, which are energized by what's called a "Driver Coil" located under the flywheel.  All OMC models that utilize points, will have them set at .020.  This point setting is usually stamped on the armature plate under the flywheel, & on the inside of the flywheel, so if you remove the flywheel you can see this setting.  If you encounter hard starting on this series of motors, you could try opening up the points a bit.  Some "Old Timer Mechanics" word is that to make those ignitions work a little better, they mechanics would open up the points to where it ran better, even about .060" as the coils lost some of their power.  This older ignition using condensers, if they start to break down, the motor can start & run for a while, but when things warm up, the condensers & coils can begin to short out & the motor may die.  You can crank until you are blue in the face but it refuses to start.  Let it set for an hour & it may then restart.  Time to change condensers.

If that driver coil starts to fail, is cracked, or starting to melt down, or whatever, there is a possibility that it would operate when cold, but fail by shorting out when heated up by the running of the motor. However do not just replace them because they are oozing black tar like goo.  They may still run for some time.

 

There is an aftermarket conversion kit available from NAPA or Car Quest that converts these early points & condenser type to electronic ignition. From the experience of a marine dealer that says it does not work well if it is being used for trolling, as it appears the RPM is so low that it does not give adequate ignition.

 

Then  from 1977 thru 1984 they have electronic capacitor discharge ignition, sometimes called a CD ignition, or as OMC calls it, Mag Flash ignition.  This has a charge coil under the flywheel that sends a small voltage to the power pack, which ups the voltage to 300 volts & is then sent to individual coils & on to the spark plugs.  From 1985 thru 1988 a slightly improved version of the system was used that was called CDII.  Then from 1989 thru 1993 another system called the UFI (Under the Flywheel Ignition) was used.