No Power under Load

[Sumo Seapro 180CC]

I need help! I have a 2002 F115 4Stroke that loses power when I try to accelerate. I can move under power at 5 to maybe 10mph at 2000 rpms but when I try to accelerate it bogs down and the average top rpms is 3000 and I am still going 10mph. I have taken motor out of gear and am able to get 4000-5000 rpms sometimes and sometimes it will not accelerate past 3000 rpms. I suspect it is one of the power packs at this point. If it is one of the power packs should I change both or just one? Any help will be appreciated. Thanks

This is what I have checked so far:

Changed the spark plugs.
Changed the water separator fuel filter.
Changed the inline fuel filter.
Replace 40 gallons of gas to fresh gas.
Bypassed the water separator filter.
Out of desperation, went to a lower pitch prop.
I have disconnected the lower ignition coil and started engine and engine idles smoothly.
I have disconnected the upper ignition coil and the engine seems to idle rough and spudder slightly.

The engine was running fine in early November and it all started when I fired it up in mid February.

[Hamfisted]

If you have a Yamaha mechanic nearby that has the Yamaha Diagnostic System software you can plug a laptop into the motor's ECU and read the computer to see what it says. Or if you wanna buy your own YDS kit it costs about $250 from the dealer, p/n 60V-85300-02. You supply the laptop. Could be a fuel pump problem or even that anti-syphon valve there at the fuel tank outlet, they've been known to fail or clog with debris from the tank thus restricting fuel flow. The dealer would put a pressure gauge on the fuel manifold and see that the fuel pump is maintaining adequate pressure throughout the rpm range. But the first thing he would do is read the computer.


Mike.......... Miami, FL

[kanco1969]

Not sure if you are still having these power issues, but it might be your fuel injectors. What you are describing sounds very much like the issues we were having with our 2003 F115 outboard. Turned out to be two bad fuel injectors.

It might also be a spun hub on your prop. When you spin a hub, you can run fine a low speed, but as soon as you throttle up the prop will spin and you will not gain any speed.