YAMAHA 2 STROKE 4 CYLINDAR NOT RUNNING ON ALL CYLINDARS AT IDLE

[Cap10Wallace]

I have a 1989 Yamaha on my guide boat and it has always ran flawlessly and is in extremely good condition. I've had it out hundreds of times in the past couple years and never had any issue whatsoever other than needing a carb cleaning and the plugs cleaned off. The other night I towed a stranded boat for several hours up river and when I got them to port my engine kept shutting off when I would go into neutral and was hard to start. I pulled plug wires off and narrowed it down to my bottom port cylindar that was acting up. If I throttle up to take off it will be a bit sluggish but planes out and runs normal. I thought it would be a carb issue so I cleaned them really well and also replaced the spark plugs. To my disappointment this didn't help. The compression is higher on that cylinder and it looks like it's "coughing" a mist of fuel out of that carb that goes to that cylinder. Almost seems like the exhaust is clogged from carbon build up. Any tips on fixing this would be greatly appreciated! Captain Wallace Sitzes

 

[99yam40]

no one but you knows what motor you are talking about, and that makes it difficult some times.
how did that plug look when you pulled it?
did you look up into that plug hole with a good light or maybe borescope?

heavy dose of ringfree or seafoam might clear up carbon if that is what the problem is.

lugging a motor like you did for hours is not good for them, that is why sea tow or other companies are called for them to pull boats with equipment that is set up for the job

 

[lakensea]

Broken reed valve.

 

[99yam40]

or lean sneeze burning fuel in crankcase, which will push stuff out anywhere it can