Yamaha 55hp won't accelerate

[birchmj]

Hi Experts...I have a 55hp yamaha that I recently put in new plugs. It starts great and will idle up fine (to high RPMs) as I increase the throttle. However, if I engage the engine into drive, it will only accelerate very little (approx 5mph). The RPMs on the engine will not come up. This is the first that I used it this year. I changed the lower unit lube before putting it away for the winter. Reverse works about the same.

 

[rodbolt]

Re: Yamaha 55hp won't accelerate

how long did it sit since the last time it ran ok?<br /> first do a compression test. then test the spark. I usually do both tests at once. if the spark will jump a 7/16ths gap and the compression is good then its time for fuel sytem maint. replace the pump and dissasemble and clean the carbs.

 

[birchmj]

Re: Yamaha 55hp won't accelerate

It ran great when I put it away for the winter in late October 04. Could over or under filling the lower unit with lube cause anything like this, or are we more likely looking at the fuel system as you suggested?