Surging engine during high RPM

[Blu]

Hi,

I'm having trouble tracking down an engine issue. The problem is that the boat will only run above 3000 RPM for about 10 seconds before it starts to hesitate and buck. I don't hear an electrical miss. Watching the tach - I will see it drop several hundred RPM and then bounce back up and all over until I drop the throttle back and get it under about 3000 RPM. The water seperater/fuel filter only has about 20 hours on it. The in-lin fuel filter is brand new and the cap/rotor/wires/plugs all look like new.

Can a fuel pump just get weak or something? Any suggestions?

Thanks for looking!
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[lovestocruise]

BLU. I had the same problem with my Port engine. It is also a 7.4 but carb. We Ckeaned the carb and re-built it and that did nothing, then we changed the coil and that did nothing. Then we changed the ICM and that did nothing. After all this it turned out that I was losing power thru the wiring harnes at high RPM's.
Take a Volt tester and put it to your coil have some one slowly rev the engine. It the tester light starts to fade I bet money that your wiring harnes has a problem and needs to be replaced.
Good luck.

 

[Asureyez]

Arching in the ingnition wires is common on older engines.