2002 Yamaha 150 2 stroke backfire and smoke

[rwerner43]

Just bought a boat today with this engine. Guy said she runs great, and was run 2 weeks ago.

She has 110-115lbs compression in all 6 cylinders.

She starts quickly but seems to run rough. Does not rev smoothly and backfires when I let off. I also get some black smoke when she backfires. One time I saw fire come out of the prop exhaust.

Plugs look dark, but clean.

Where do I begin?

 

[steelespike]

Re: 2002 Yamaha 150 2 stroke backfire and smoke

Speaking generically;
I think I would start with the ignition; be sure the wires are on the right plugs.
Also see if squeezing the primer bulb makes it seem to flood;could indicate it needs a carb rebuild.

 

[erniefish]

Re: 2002 Yamaha 150 2 stroke backfire and smoke

backfire usually is a sign of a lean fuel issue(clean carbs) ,plug wires are easy to check,do not assume they are on the correct plugs, check them.also check to see timming advances when throttle is pushed forward,thats all i can think of right now,