1999 Yamaha C40 top end miss

[ddhuntermark]

I have a yamaha c40 that runs fine at idle and up to 3/4 throttle. When I give it full throttle it will occasionally hesitate or almost like it is missing. New fuel bulb and line, sprayed carb/engine tuner into the carbs, new plugs, new gas. It still hesitates and will not run at full power. Seems like it is only running about 3/4 throttle. This started about 2 weeks ago.<br /><br />I follow all the recomendations for full stabilizer and ring free additive. The engine is used at least once every week but this problem started after it sat for 2 weeks.

 

[redyute]

Re: 1999 Yamaha C40 top end miss

i had a similar problem and when i trouble shooted it i found that i had a bad fuel pump diaphram.You propaply should try a fuel filter reduild if you haven't done so.

 

[redyute]

Re: 1999 Yamaha C40 top end miss

fuel pump rebuild sorry

 

[ddhuntermark]

Re: 1999 Yamaha C40 top end miss

Thanks for the reply. I was thinking about trying that first. How hard is to rebuild the fuel pump? Just looks like a couple of diaphrams.

 

[ledgefinder]

Re: 1999 Yamaha C40 top end miss

Try squeezing the fuel bulb while it's happening. If the problem goes away, you know it's fuel starvation, most likely fuel pump.