1986yamaha9.9
New member
Hello, I have recently bought an older Yamaha for my aluminum boat. I had some trouble getting it started due to a sheared keyway on the flywheel. Now that that’s fixed it starts first or second pull, idles great and was pulling hard for about 5 minutes until it started chugging and stalled (almost like a misfire). Started right back up but it would start chugging every time I tried to get off idle. Shutting the motor off for 10 mins will give me another few minutes of full throttle before chugging again. Pumping the fuel ball made no difference, cowling on or off made no difference. Once I got home I checked the spark plugs (they were new prior) and they were totally black, bottom cylinder was worse than the top. I figure it’s running way to rich at higher rpm. It idles very well. I’m not sure what the issue could be. The carbs were cleaned before I got it running, it’s fresh ethereal free fuel. My only two ideas are there’s an air/fuel adjustment I can’t find or someone has put a larger main jet in the carb. Any suggestions will be much appreciated, thank you.