1984 Yamaha 40hp 2 stroke smoking at idle

[ChrisMA]

I have had this engine for around 8 years and just recently I have noticed that is smokes at idle. Starts right up, runs strong up to redline, but when bringing back down to idle is blows smoke. It has never done this before, generally at idle there hasn't been any smoke at all.

Does this mean I could have a tear in my oil pump diaphragm? It doesn't look like you can buy a rebuild kit for the pump, is that the case?

What is the harm in running it smokey? Burned out spark plugs?

Chris

 

[ChrisMA]

Re: 1984 Yamaha 40hp 2 stroke smoking at idle

Any hints on this one? Where do I start?

 

[GrayBlue]

Re: 1984 Yamaha 40hp 2 stroke smoking at idle

Could you premix for a day and see if that cures it? If so then at least you know it's pumping too much oil. If that doesn't cure it I would think you've got a lot of carbon build up. Have you used seafoam before?

 

[robert graham]

Re: 1984 Yamaha 40hp 2 stroke smoking at idle

Maybe when you're running wide open throttle and about 30MPH, you don't see or notice the smoke, but at idle you're not moving much and the smoke becomes noticeable. My 90HP Yamaha premix 2 stroke smokes some at idle. I switched to the Pennzoil 100% Synthetic outboard Oil a few years ago and it seems to smoke less, burn cleaner, less carbon. Maybe your fuel pump is going bad, sucking raw gas into that cylinder causing rich/smokey mixture. Check fuel pump and spark plugs for rich, fuel-wet conditions. Good Luck!

 

[ChrisMA]

Re: 1984 Yamaha 40hp 2 stroke smoking at idle

I have used seafoam before, I usually add some to the fuel. I like the idea of running on premix, should it be 50 to 1 for this engine? I am also going to make sure the oil pump linkage hasn't come disconnected. I was reading the shop manual and this looks probable as well. The oil pump is gear-driven and I highly doubt the pump is bad.

Robert, this is a night and day difference, that is why I noticed it. I basically went from no smoke at idle to smoke more or less pouring out of the 2 ports high up on the rear of the leg. I would think carbon fouling would start gradually? Maybe I will also spray seafoam directly into the carbs?

Thanks for the hints!

Chris