Fishing forum > A Non Smoker

Author Topic: A Non Smoker

A well serviced two stroke outboard does not smoke.

However, it has to serviced, and I have never seen coils in such a bad state. I even found some insect life in there. I am looking forward to ice off Yellow Lake in a couple of weeks, and just so you know, my primary drive is a Minn Kota.

"A well serviced two stroke outboard does not smoke. "

Really? Did you remember to "mix" the gas? An old outboard SHOULD smoke because of "rich" the mix ratios. Even my 100:1 Yamaha pushes significantly more smoke than a 4-stroke with bad rings.

You are totally correct, and to be quite accurate, every internal combustion engine must emit some pollutants. But these can be minimized.

If your outboard noticeably smokes then it is time for a service, but if it is in a good state of tune, then nearly all of the gas/oil mix will get burnt. Using a good quality two stroke oil for cool running engines will also go a long way to minimize any damage done to the environment.

I guess, also, that you are likely to put out more pollutants in driving to and from a lake, than by a few hours of gentle trolling around a lake.

unless you have an electric trolling motor. My yamaha is run at about 75-1 since I am leery of going 100-1.

Any older, non-fuel injected 2 stroke, will smoke and there is nothing you can do about it. Combustion of the oil in the gas makes these older two-stroke engines smoke.

Also a point to add to this: The fact that they have a time within the stroke when the exhaust port and intake port are open at the same time. This causes oil/gas mixture to go out the exhaust port un-burnt and more smoke to be produced. This is called scavenging.

Edzzed, as long as you are running a good quality oil, there should be no problem going to 100:1. If you are oil obsessed, Amsoil makes a 2-stroke oil that they claim will do everything but cure cancer. I might be running mine a little richer than 100:1 but have been having a fouling problem because I think someone monkey'ed with the carb jets. Still sorting that one out, but think I need to do a major carb rebuild. Had the carb apart numerous times and the issue still eludes me...

could be that the gas /oil mixture is old.? gummed up a system or two that way,grabbed the wrong fuel tank a couple of years ago!!! every day i was cleaning plugs / carb out:/ended up rowing the lsat two days

Fouling can be caused by a number of reasons, the most obvious is excessive oil, incorrect oil, stale gas/oil mix, incorrectly adjusted carb. But can also be caused by poor spark or incorrect timing, and low compression. All these mean that the mix is not fired properly and will leave excess carbon in the combustion chamber and thus fouling, not to mention an obvious trail of smoke.

Some outboards do not run well at low rpm for long periods of time so it is good also to run your outboard on full throttle for a while to get the motor up to temperature and burn off some of the deposits.

Back to the beginning here and a well tuned two stoke should not noticeably smoke.

Thank you all for your comments.

I think someone drilled out the main jet...thinking that bigger jet = 10 more HP (on a 2HP). Because I have checked everything, the jet number is even correct. This thing has low hours etc etc. The spark is strong, the plug is correct, the fuel is new, the mix is correct and the compression is strong. There is no lean-rich adjustment, so there is not much else it can be. Guess I will order a jet and rebuild kit and cross my fingers because even the float and needle are in great shape. Buying a carb is pricey for such a basic motor or I would have just got a new one.

Not that you would not have tried, but it is worth mentioning the float level and the pressure return valve in the fuel pump, that is if there is one.

I can't think that somebody would have drilled the jet out, but you need to be sure there is no mixture adjustment and many carbs have both a slow and a fast running jet.

Back to the Johnson of mine, it does not have a fuel pump, instead it have a air return system from the motor to the tank and pressurizes the tank to force the fuel back into the carb. This is considered rather dangerous as if there is an air leak from the tank it will be expelling an explosive mix. Then I can say "no smoking" when using this outboard.

I'm not sure if we covered this or not Mr Jeff, but I actually am a mechanic and make my living primarily that way. That being said, I mostly work on things that have wheels, so I am not a marine expert and am always open to learning from others that have knowledge to share. I have done marine work on things much more complex than this motor and I have to think that there is something fishy here (tampered jet). As you can see by the photo, this carb is about as basic as it gets. As we covered earlier, other common novice mistakes have been eliminated. I have had this carb apart about 3 times trying to get to the bottom of the issue prior to just "throwing parts at it". There is no mixture adjustment and I do have the factory service manual for it, which is where the photo here came from. All I know is that I would rather paddle than carry a 6-pack of spark plugs and keep rotating them in a jar of solvent. Any ideas anyone?


Here are a few things, other then the main jet to look at.

-needle and seat leaking.
-float setting.
-Choke still on a bit (bent etc.)
-worn/wrong/Damaged idle srew
-or needle jet issue etc..lots of things really.

also what spark plug are you running right heat range etc... 2HP yam should have B5HS

Good luck!
or just send me it and i'll fix it up for up lol
I'll look around the shop see if I have a old carb I can send you as well.

Also just because it has good compression doesn't mean that the rings and piston/ bore are in good shape...the oil in the gas helps to seal the rings and not producing a fare test. I have seen many 2 stroke engines torn down that have had good compression but have cooked pistions/rings etc. I love my little borescope for checking out the inside.

Curious about the idle adjustment screw. Does this hold the throttle valve open or does it control fuel flow at low revs? I can't quite make it out from the picture.

Catch: I'm pretty certain I have the correct plug(s) because it even still has it's original plug decal. On that topic it has been gapped correctly too. I just got a good shop manual for it so I am going to go over everything and rebuild the carb when I get to it. I just did not go too deep like checking the ignition etc because it was given to me and hardly looked used. The thing looks new and everything is tight, besides scuffed side covers from the shelf time that had likely made up most of its time. The internals in the carb look pretty decent too but now that I have real specs I can go over it all. The choke like the rest is tight. A few things to go over. Thanks for all your help too. On the topic of bore condition, I worked doing a lot of small engine in the equipment rental industry, so I've seen some things you wouldn't believe. I am almost certain compression is not an issue, but I'll check that also (without soaked rings). Oh and I think I'll pass on just giving it to you, I catch more fish in my canoe than any other way, so I need this thing to be reliable instead of a frustration. I go fishing to escape work, a canoe should not contain a toolkit and solvents.

MrJeff & Catch: Idle screw doesn't do a heck of a lot on this carb but prop the throttle butterfly open and that it accomplishes. Sorry to 'jack your thread, but it is on topic, civil and productive unlike most threads.

The only other thing I can see is the height of the needle, it does not look adjustable but it is difficult to make out from the drawing. If not is there any way it can be set a little lower, thus weakening the gas/air mix. On such a small carb even a small adjustment will make a big difference.

Apparently it should be in the "low" position for regular altitude (have to confirm this is indeed the case) and higher for high elevations. They mention a moveable circlip. This will be one of the things I check when I get around to ordering the carb kit and redoing. I really just got sick of it an shelved is supposed to be a Yamaha=reliable. I was about ready to trade it for a Seagull this winter.

ChakaRaka: Hey I didn't mean I was going to keep it; just fix it for you. (its what I do for a living) Have a good one buddy. Sounds like you've got a lot of know how so I'm sure you'll get it beat.

OK, I would definitely go for the circlip, and if the drawing shows what I think, there are several grooves in the top of the needle that allow for it to be set a little lower, thus achieving a leaner gas/air mix.

A word of warning to others who may not be so technically minded, if you go too lean you could seize your motor, please don't mess if you are unsure of what you are doing, seek professional help.

Oh, yes, is that really him!

scary site. next thing you know my photo will show !!(if my satelite ever allows me to download !)

Mr Jeff, I have to give you "props" (seemed fitting slang when talking about motors). You were on to something. The only part I did not take apart was the throttle valve. Within that is the needle that you were referring to. The e-clip is was set to the standard position and had one adjustment higher (on the needle, which would make it lower) which would be leaner. The intended use is for high altitude operation. But here's what gets me, it has 2 adjustments lower than standard (which would be richer). Not sure why you would ever need it that rich, forced induction maybe... [scratches head] So I adjusted it leaner and ran it in the bucket for a couple hours. It seemed to surge a little at WOT, but seemed about ideal for low throttle operation. What I have concluded is that the needle is worn and sloppy. I am under the impression that it is not just the cone/seat that control fuel, but also the shaft diameter of the needle. I will order a rebuild kit and address this, but in the meantime it seems to be running better. I will not know for sure until I test it out for a day on the water.

I also looked into the float more, but it and the hinge are one plastic assembly and I do not see how it can be adjusted for float drop. In addition to that, it appears just slightly different than what is shown in the manual and does not seem to match up with either of the two specs provided.

This is a 1989 2sf model and I am looking for a place to get a good price on the rebuild kit. Does anyone have any suggestions for this side of the border? I found a place in Washington with a great price, but am worried the price will double when it crosses the border...

I do use a quality 2 stroke smokeless oil but even at 75-1 I still see it. I would have bought a 4 stroke but for power to weight there is no comparison there. And since I gotta lift the motor off the truck to the boat and back, well lighter is better. I know I could use my automatic boat loader to do it but seems it takes to long and I'd have to build a slide out for holding the motor rather than what I currently use. Comes down to space in the truck.

What brand are you referring to if you don't mind me asking Edzzed? The rest makes sense, 2-strokes don't mind being stored on their sides as much as 4-strokes too.

did you solved the too rich fuel/air mixture for the Yamaha 2HP? (2BMH)
I have the same engine with just the same issue,I bought
it brand new 12 years ago and it always gone too rich since the first day...At half throttle I empty the fuel tank (1,2 L) in less than 20 min.!!!!
I now decided to try fix and searcing the web I founded your post about...
I confirm that the jet needle can be lower only one groove
I did it and it runs much better.
To add something I also lowered a little (less tham 1mm)the fuel level in the bowl heating gently and then bending with plier the plastic seat where the needle valve goes.Just a little!!! The jet needle must remain "free" into its float groove.
Next will be trying to prop it with a lower pitch prop but
there is nothing smallest than its plastic one!!!
I strongly suppose that we all overload it and it helps to foul the plug.
Sorry for the poor English language,I am from Roma,Italy

I use Amsoil. It is supposedly one of the best on the market. One trick I learned is when the wind is blowing at trolling speed, I turn into the wind. Any smoke then leaves to the rear. The motor is also a 2008 and even sitting for 6 months it will still start on the 1st pull.


I got really busy with work and have not had a chance to get it out on the water and test it out yet. If it doesn't get cold too fast, I will try it out and see what happens. This one really has me confused because it has never run correctly. And as you have likely found out, there is little information on the internet about this problem considering lots of these motors were sold both as Yamahas and Mariners. If I ever get it solved and running well, I will post my results and "fix" here. Let me know if you find any other info on this yourself.

I suppose that most of the users simply do not mind at the problem,at least it runs,starts always and easy,and after a couple of minutes or so at more than half throttle it begin to run a little better.
I will contine to work around it as I want to solve the problem before next summer and I will report the results.
Now I am trying to find or build a sort of test propeller to test any modification it in my garage.

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