1997 40hp 2 stroke smoking bad

[Justinskywest]

Thanks for taking the time. I have a 97 40hp 2 stroke that starts right up and runs like a top at high rpms, but loads up on acceleration from idle for a few seconds, then it clears out and runs like a top. I've replaced spark plugs and it helps for the first run, but always reverts. The motor also smokes more than normal no matter what fuel mixture I run. I've found that 70:1 has been optimal for me, but I've tried 50:1 and even 100:1 once. It pinged at 100:1 so i added mix to bring it back to 70:1. I ***** for salmon all day long just out of neutral and sometimes that smoke is just too much. Please help

[boscoe99]

An acceleration issue would lead me to believe the carburetors need an adjustment, or cleaning and an adjustment.

Fuel/Oil mixture is not the same an fuel mixture i.e. air/fuel ratio. If the motor is leaned as much as possible (leaner air/fuel ratio) to eliminate smoke it may very well not accelerate as well as it will with a richer fuel mixture.

Re the oil, if you are using Yamalube it is known to burn dirty. Maybe try Pennzoil semi or 100% synthetic and see if your smoking issue is mitigated.

I will take two fat sockeye please.

[robert graham]

Maybe check for a hole or crack in fuel pump diaphragm causing raw fuel to be sucked into engine and a rich/smoky mixture and some rough running....remove pump with 2 hex screws while leaving fuel lines attached, then pump primer bulb and look for fuel coming out of back port/hole of fuel pump...should be none.

[99yam40]

*****ing all day is tuff on a premix motor's plugs.
the oil injected ones are able to cut back on the oil at lower RPMs where the premix cannot.
then when you hit higher RPMs the extra oil is really needed, so lowering the mix may not be good.

Check your fuel pump and maybe the recirculation check valves that are on the lines coming off the crank case.
I found several that lost the checking ability when I redid my 1999 40, so the puddled left overs in crank case was not being sucked out.

Just a thought

[Justinskywest]

I appreciate the help. I'm planning on trying to lean it out a smidge tomorrow and see how she performs. Since the fuel pump diaphragm sounds like an easy check I'll do that first and go from there. I'll repost after I take her out and provide some feedback. Again thanks for your time. I catch Chinook and Coho here on the Southern Oregon coast, so no sokeye. We go for the big ones here

[Justinskywest]

Is it possible to add the oil injection to my motor?

[throrope]

I thought all the three cylinder yams were oil injected vs. premix. If yours is oil injected sounds like another ethanol issue.

[Justinskywest]

I premix my fuel. Non-ethanol premium and yamalube

[99yam40]

I thought all the three cylinder yams were oil injected vs. premix. If yours is oil injected sounds like another ethanol issue.

the C40s are premix
If the posters would post their motors model number it helps others know what they have

Oh to the op,
I believe it would be not cost effective to change it over even if you could.

[throrope]

the C40s are premix

Thank you!!

[Justinskywest]

Copy that sir.

[TownsendsFJR1300]

If it ran good prior to this, re-jetting isn't needed.

If the carbs were clogged, it'd lean out from lack of fuel, NOT load up with extra fuel (unless you have a sticky float (in the carb-IF equipped)

Agreed with Robert, a leaky fuel pump would suck excess fuel / oil into the crankcase.

I would NOT dink with changing your pre-mix %. It worked fine before, you should NOT have to change it now, find the issue..

Good luck

[Justinskywest]

I bought everything to do a full service today. Hoping to get my hands on a carb sync guage tomorrow. My plan is to pump out my fuel tank and go with a 50:1 and lean it out till it runs properly. I'm not too concerned about dirty carbs as I've always run clear gas and treated my fuel before storage, but I'm more than willing to tear those bad boys apart and give em "what for". Either way i plan on making sure they are synced. I am subscibing to the school of thought that having a premixed system does affect the ability to clear out the abundance of oil on acceleration after long *****s at idle. As long as I can get the smoking under control I'm fine with the way it's operating. I just want my wife and baby to join me this year.

[ausnoelm]

I guess you didn't read the bit where you were told NOT to play with leaning out the oil mix! It is 50:1 leave it that way, using less and less oil is just a method of finding how little the motor will run on before it stuffs up, and when you find that point, it's too late.....

[TownsendsFJR1300]

IMO, (and Roberts), it doesn't take several minutes to check for leaks with the fuel pump and NO cost..

Although NOT your problem, you may consider synthetic 2 stroke oil which should give you better protection (at the same mix) and likely will smoke less