Hi, I am having a loss of rpm's. The engine starts right up,idles fine,takes off fine. When the engine is running wide open at 5900 rpm's and gps speed of 64 with two people and a tournament load, the engine will slowly start dropping rpm's, all the way down to about 4900-5000 rpm's. Anyone have any idea's about what could be causing this problem. Thanks

That could be a lot of things. Could be a coil dropping out after it gets hot. I have also seen where one cylinder doesn't get enough oil and the piston expands and causes something similar.

VST pump screen, Fuel tank vent, or a fuel line bent-kinked. Could be the fuel pickup screen in the tank. I am seeing a lot more problems with the anti-syphon valve.

Thanks for the responses. I'll have them checked out.

If its a ox66, have the O2 sensor checked/cleaned/replaced.

Thanks, It is a ox66.

My guess is fuel pump diaphragms. I have the exact same engine including year. If you let it go, it will get worse and finally won't run with any kind of load. That's how i found out! Easy to change and not expensive. They are a brittle clear plastic and I have had to change them out twice in 6 years.

I would think that it is a fuel restriction causing you to loose power. I would change all the filters, primer bulb, check the anti siphon valve at the fuel tank. But mostly. I would do the two filters between the VST tank and the Electric fuel pump. In my area those are the two that is giving the most problems. Then do or have a fuel pressure test done at different RPM's.