Yamaha 150HP 2.6L V6 looses rpm

Hi Guys,*

I was wondering if anyone can help me, we bought a speed boat (second hand), all was great on the boat but thought we might as well send it in and give it a full service *( replacing the spark plug, filters etc. ) .it went well for the first few trips to the dam up until now! When the boat is at top revs 4700rpm it suddenly drops to 3700rpm. I then stop the boat and when i pull away again it goes like hell for the first few minutes but then suddenly the same problem occur? Can somebody please give me advise on what the problem could be or offer a possible solution?

It would be of great help.
Regard*

I do not know what the year model number of the engine is, Yamaha 150HP 2.6L V6*

Can you pump the fuel line primer bulb firm ? If not I would look at the fuel pumps (there are two on the port side of the power head...). They generally last about 5-6 years before they need to be replaced. Do you notice a miss when the rpms drop ? Or is it just a general but otherwise smooth slow down? If you detect a definite miss then I would look at one or more of the coils going bad. But it sounds to me like you're describing a fuel issue. Good luck.


-Mike

But are using fuel pumps good because when I tried it they had very bad effect on mine.

motorcycle transport

If you are at 4700 rpm your pitch or diameter is far too big at wide open trottle.Otherwise you gotta Carb issue,especially if you have EtOH gas and you aren't anal about your gas filtering, I mean ANAL!

Good karma !