1986 johnson 9.9 hp 2 stroke

I just purchased this motor and it has only been tank run so far. There is a sticker on the cowling by the gas hook-up that says 100:1 mix. The guy I bought from said the guy he bought it from it said to mix it 50:1 and add a third of a can of seafoam. When the motor was started and even after ir warmed up, I could have fogged for mosquitoes (if there were any). Any thoughts on this particular motor?

Hi, check the thread on 1970 Johnson 25 smoking. This applies to your motor too. I run Amsoil at 100:1 Premix in most all my newer motors. You can safely go to 100:1 with that in your motor but non oxy fuel only. When OMC recommended 100:1 mix in those days, there was no ethanol yet. Ethanol becomes separated in time and the octane will stay with the ethanol as well as any moisture that may have entered the fuel. The ethanol will suspend its own weight in water and in time that will cause the separation. Once the bond is broken, you get the ethanol, water, and much of the octane at the bottom of your tank. The sad part is that it still will burn, but messes up the mixture creating a less volital substance. This mixture is not meant to be introduced into any combustion engine, but happens quite often when ethanol approaches 6 months old. Sometimes the water is suspended in the fuel right from the pump and we don't know it. It burns fine, but it will separate faster, the more water that is suspended. As the ethanol ages, it becomes unstabil, that's why your seller likes to use Stabil, to slow down the fuel deterioration. If you use pure petrol (non oxy), Stabil can still improve the life of the fuel sometimes to 10 years in a good storage tank. Ethanol is pretty stale after about 1 year with stabil added, unless it is in an airtight container, not exposed to any moisture in the air. This is part of the problem that will act like leaning out your 100 to 1 and cause scoring because octane actually "tames down" the gas in order to stop pre detonation. This is especially a problem with older engineering that doesn't detect the problem and adjust the timing like computers will do on your newer vehicle.The oil recommended at that time OMC was experimenting @ 100:1 was not nearly as good as they thought. There was no margin of error in case of improper mixing. They stoped recommending 100:1 as motors were getting damaged. Also the injection fuel tanks at 100 to 1 were discarded. Those tanks were not a good idea and toasted plenty motors.

jerky man said:

I just purchased this motor and it has only been tank run so far. There is a sticker on the cowling by the gas hook-up that says 100:1 mix. The guy I bought from said the guy he bought it from it said to mix it 50:1 and add a third of a can of seafoam. When the motor was started and even after ir warmed up, I could have fogged for mosquitoes (if there were any). Any thoughts on this particular motor?

Click to expand...

In 1985 OMC switched to 100:1 for their premix motors

After 2 or 3 years worth of failures and warranty claims they switched back to 50:1 and issued a service bulletin advising that all those sold as 100:1 should be switched to 50:1, that 100:1 stickers should be removed and handbooks amended.

The correct mix for your engine is therefore 50:1 using a TCW3 certified 2-stroke outboard engine oil.


After tank running it will smoke a bit until all the unburnt oil in the engine is burnt off. If you have added anything extra it will smoke even more. Get it out onto a lake or the sea with some fresh 50:1 and give it a run at a good speed and the smoke should soon clear,

Cannot comment on the use of Seafoam specifically but the use of a fuel stabiliser, such as STA-BIL®, especially if modern high ethanol content fuel is to be stored for any length of time, might be a good idea.

There is no difference between the 50:1 motors and 100:1 models as far as parts go.-----The board room / marketing folks decided on this.-------Simply to try and retain market share.-----The public believes that a motor that can run on less oil is a " better built " motor.

vics said:

In 1985 OMC switched to 100:1 for their premix motors.....After 2 or 3 years worth of failures and warranty claims they switched back to 50:1

The correct mix for your engine is therefore 50:1 using a TCW3 certified 2-stroke outboard engine oil.

After tank running it will smoke a bit until all the unburnt oil in the engine is burnt off. If you have added anything extra it will smoke even more. Get it out onto a lake or the sea with some fresh 50:1 and give it a run at a good speed and the smoke should soon clear,

Cannot comment on the use of Seafoam specifically but the use of a fuel stabiliser, such as STA-BIL®, especially if modern high ethanol content fuel is to be stored for any length of time, might be a good idea.

Click to expand...

This is all correct. Use 50:1 on this engine. I use Evinrude Premium 2-stroke oil (the red stuff) that I buy at Walmart for under $20/gallon. It works perfect in my 1979 Evinrude 9.9 and I have minimal smoke from this engine.

1/3 can of Seafoam in 6 gallons it a bit much. I use StaBil Marine 360 on each fill up and that works just fine.

As Vic said, if the engine hasn't been run for a long time you might have excess fuel/oil pooled up and just needs to burn off.

You can do a couple of things to make sure the engine is completely healthy.

1) Replace spark plugs
2) Ensure you have proper spark. Use an air gap tester and make sure it jumps a 7/16" gap.
3) Make sure your low speed needle is set properly and that the carb is not running rich at idle.
4) Use a ratio mixing bottle (about $3) when adding oil to your fuel. More oil IS NOT better. A 50:1 mix is perfect and all that you need. More oil just means more smoke.

Nothing I can add to the above... Just stick to the 50/1 mixture.

Great advice all. Now where is our boater? Did any of you ever think that OMC was trying to "push" the mixtures in order to clean up the bad rap that 2 strokes were getting on polluting both the water and the air? 4 strokes by other manufacturers, mostly Honda....here in the US, [I bought one for my Dad (pictured), for his trolling motor used for his fishing guiding], were the wave of the future. Now how can we make them smaller and lighter with all these moving parts? I truly believe that OMC had this in mind as well, while laying a platform into the 4 stroke market. !00:1 had been used by my Dad and myself already for about 8 years in all our 1965 and newer motors with leaded fuel at both our Ontario camps. We accepted that OMC must have made some engineering changes in order to recommend 100:1 without specifically calling for Amsoil fully synthetic 100:1 which by 1985 had become quite popular. In order to minimize emissions....namely smoking.....we continued to run the 100:1 Amsoil with great results as well as happiness of our guests to breathe fresher air around the boats when trolling. Mr. Al Amatuzio, Amsoil's founder, was a great friend of my Dad and wanted us to experiment with 100:1 even in our pre 1965 motors. We have a few early 50's 5's and 3's on our portage lakes. I told him, no way, but would try 64:1.....thats 2oz. per gallon. Also ran that mix in my power equipment that was air cooled. Al said go to 100:1 and I will replace anything that breaks as a result of lubricating fault. I never did and to this day, (Al died in 2017), never tried 100:1 except in my 1969 Ski Doo 12.3 Olympic. I logged many hours on that old 12 hp up in the frigid cold of NW Ontario as well as warm April ice fishing trips where sometimes we hit 70 degrees. Never had a problem with that old German Rotax. That Ski Doo is still used today, every year, and still as sweet running and clean as ever.
With so many 4 strokes out there now, I continue my 2 strokes and really don't want any complaints from smoke. Not only from customers but from observers. If those like me, who embrace the rock sold technology of the 60's and early 70's, dont move to reduce the smoke and emissions from these 2 strokes, we may soon see legislation.....like in California.....to ban these reliable, efficient 2 strokes from all US and Canada. Having said that, I am still running either 100:1 and 64:1 in ALL my outboards, right back into the 60's vintage. I am still waiting to have to rebuild one of my own outboard's because of lack of lubrication. I also recommend any motor, (2 stroke), that leaves my shop, that is 1965 or newer, that the owner will get a free quart of 100:1 pre mix Amsoil and a 1 year warranty on my repair. they are instructed to mix at 64:1 and can go to 100:1 if they are mostly trolling.....like on the kicker motor. And NO ETHANOL! I have done this for hundreds of repairs over the last 25 years with only 1 comeback. That return was because of an unknown overhauled 1960 10 hp that I got from auction that could have had a problem with either a mixing issue or a pre existing condition that I didn't pick up on. The guy never brought the motor back so I could do a teardown exam, just returned his money in another deal. He is still a friend.......and no, Mr. Scott, I have no stock in Amsoil. Al was just a great friend and a guy who changed the lubrication industry forever and for the better.

p.s. Hi Joe, you wrote while I was typing.