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9.9 1974 Johnson Heavy Black On Plug

The newer motors had bigger wrist pins.-----Clutch dog had 3 lugs instead of 2.-----And yes with proper care a 77 model will run for a long time !!
 
So, doesn't Patiolatern get an award or at least an honorable mention for 'sticktoitivness'? Holy crap, talk about the proverbial dog with a bone!!!
My hat's off to you sir.
 
I'll say, its gotta be a record thread. Thanks for that info, Racer. The 33 cu in went to 3 dog after a few years too, was it 1980? Prop shafts changed at that time to 1 more spline, or was it one less. Guess just so you couldn't interchange with the 2 dog shaft. Personally I never broke a 2 dog anyway, or never had rod or wrist pin troubles with the early 9.9/15's. Musta been the 100:1 Amsoil? Still running 3 pre 77 15's at camp.
 
Other then the spark plug fouling issue I have gotten great use out of my 1975 9.9Hp and my 1976 15Hp for almost 2 decades. They are wonderful motors with lots of power and usually start on the first pull. I use the NGK spark plugs and have gone to the B6HS (a little hotter then the B7HS) spark plugs and never really had any fouling problems after that. I prefer an electric for trolling so I don't do a lot of that and I make sure the T-stat is working and my rich/lean is set properly. I still change the spark plugs every other season as regular maintenance and never had any big problems from them.

I will add that where I got confused on this thread was when I was personally navigating the spark plug fouling issue I had with mine, each time it happened I only fouled one plug at a time. In other words the bogging down and all that was the same but my motor never died completely and if it did it easily started back up and always got me back to my dock on the other cylinder. It also NEVER passed the cylinder drop test when I tested it at the dock. I use to keep a spare set of spark plugs in the boat but never needed to take the time to change them in the water because the motor was still running. In Patio's case it appears that both spark plugs failed on the same trip and that was such an outlier for me that I did not focus enough on the spark plug fouling answer.
 
Perhaps my good performance over the years with these motors has been 100:1 on Amsoil. Simply never foul spark plugs. And yes proper operating temperature and a fully functioning thermostat is also of key importance. These motors are trolled for hours on end for lake trout at 2 mph on a 16' boat.
 
As I said, over a quick learning curve my outboards started to perform much better. The first experience of fouling was when another mechanic mistakenly put in some QL77J4C spark plugs. As many know that plug was specified by OMC for most motors after 1977 until mid 1990s, so it was probably an educated guess, that unfortunately was wrong. Those spark plugs did not last the week. Way too cold of spark plug for the 1974-1976 series IMO.

I then went to the specified champion spark plug (UL81C) and within a month or so I was replacing those. I then proceeded to ensure my rich lean was set right, my T-stat worked properly and the motor was properly decarbed, so when I switched to the NGK plugs (B7HS) and stopped trolling with it, things got a lot better for it. Then a couple friends borrowed the 15Hp and trolled for about 3 hrs and the next day, sure enough, I had one fouled spark plug. I don't know how old those spark plugs were before the trolling but I doubt they were more then 2 years old.

So that is when I stopped all trolling with it and switched the 15Hp to NGK B6HS spark plugs and I have never fouled a spark plug in over 15 years. The motor starts on the first pull and pins me to my seat when I open her up WOT on my 14 foot boat.
 
Okay a couple questions. What are you gapping the plug at, what type of oil are you using, what is your mixing ratio, is your spark advancing enough before bumping up the carb? Lastly are you using non-ethanol fuel?
 
Plugs get gapped at 0.030". As for Oil, the cheapest TCW3 oil I can find mixed 50:1 or a little more, perhaps 40:1. My link and sync is set about as good as I can get it. I use the regular gas out of the pumps. It says it might contain alcohol. Whether it does or not I can't say but I am not going to use high test.

Keep in mind these motors are almost 50 year old. They are just not worth enough to put high end oil or gas into them and I can't be sure it would make much difference anyway. As I said, the fouling problem for me has been resolved. Whether they can be made to troll well or not makes no difference to me since I have an electric trolling motor that I prefer to use for that purpose.

My point with this thread is to point out to others that if you are looking for a motor and plan to do a lot of trolling with it, I would suggest not buying a 1974-1976 9.9/15Hp Evinrude/Johnson. If you already own one, then this is what I have done to make it work
well.

I also have a 1990 15Hp that I tend to use more these days. I still don't troll with it but what I like about it is the throttle cable as opposed to the throttle gears found in the older models. Those gears eventually result in a lot of play in the throttle and that can become annoying if it gets too much play. Mine have.
 
Yes, fuel DOES make A difference, so does oil. Alcohol will damage anything with rubber composition, as well as many synthetic materials. Alcohol will draw in and suspend moisture, causing early fuel spoilage. For what little the motor uses in fuel....plus you gain 3 to 5% power, its frugal and wise to buy fuel thats not contaminated with a hygroscopic material such as ethanol. Ethanol is best left in whiskey, not in the gas tank.
 
Also I recommend gapping these plugs at .025 and I have had great luck with the proper Champion plugs and the extremely high quality fully synthetic Amsoil 100:1. With this advice there's no reason that these motors cannot troll all day long and have spark plugs last for a full season or more. Been doing this for 40 plus years up at our remote Ontario camps where we supply boats and motors for guests. Great job on the thread and thanks for hanging in there.
 
Thanks for the suggestions.

I would have thought that if one was going to change the spark plug gap that going towards 0.040" would have produced better results. More of a guess on my part then anything well thought out. What is the thinking behind the 0.025" gap?
 
The combustion chamber on the head wasn't redesigned until 1977 and then the .030 gap is fine. I have just had very good results at .025 with the early class 9.9 and 15s
 
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