Power loss on a good engine??? 97 Yamaha 115

[Matt1399]

I have 1997 Yamaha 155hp two stroke. there is reduced power and she runs slightly jolty at idle. She normally tops out at 36 mph but now only about 25. I checked the compression and all four cylinders are right at 130psi. Replaced all the spark plugs. I did the remove the spark plug wire test to see if the engine bogged down and it did on all cylinders except one. That cylinder plug will still create an arc from two inches away. What does anyone think?? thanks

 

[rodbolt]

Re: Power loss on a good engine??? 97 Yamaha 115

sounds like clogged carbs and/or a faulty fuel pump. if spark is good and compression is good usually its fuel. its routine to toss and replace the fuel pump every three years. it does not last forever and can cause major engine failures.

 

[JB]

Re: Power loss on a good engine??? 97 Yamaha 115

Yup. As Rodbolt says: Carb trouble is most likely. Don't agree on fuel pump, though; because I think that would affect all cylinders, not just one.<br /><br />There are other possibilities. A bad reed, loss of crankcase compression by a bad gasket on the reed manifold or bypass cover.<br /><br />Good luck, and let us know what you find.