Yamaha 40 hp loss of power at wot

[Leeds]

Still have this problem: 1999 40HP. At wot, runs fine for a few minutes, then loses power (5500 rpm to 5000rpm). If I throttle back, it will surge and run fine for another few minutes. If I do not throttle back, it will continue to lose power and stall, but start back up.
I have: Rebuilt carbs twice, changed fuel pump, filter, tank, fuel line, fuel, plugs, prop, fuel lines, gages. Now oil alarm goes on for no reason, but turns off if engine is tilted up then down. (sometimes). Oil sensor seems to be OK mechanically.
Should this engine become a mooring, or is there hope?

[jonp]

Leeds,

I think there is hope... May be dirt and grime in the sensor. I have a 90 HP with an internal oil tank. I also have spare. The spare was stuck. This can cause a faulty reading if the float does note move up and down freely. Is it possible to take out the sensor for cleaning with out making a mess? Also check all wiring connectors, make sure nothing is loose before you do anything.

As far as loss of power, sure sounds like a fuel delivery issue.

[Leeds]

Jonp:

Thanks for the reply. The sensor float did move smoothly up and down the shaft, however,I did not do more than manually make it move. The next step may have to be taking it out and give it a closer look.
As far as fuell delivery, when the hesitation does start, the bulb is still hard, and squeezing it has no effect.

[NealZXclass]

have you checked the compression/ ive noticed that if it changes 7 to 10 pounds per cylinder on a yamaha sometimes it is as simple as changeing the head gasket.

[Leeds]

I'm willing to check almost anything. A compresson check makes sense. Thanks! I'll post the results.