Mercruiser 350 Mag ignition problem?

I have a '97 Mercruiser 350 Mag (Serial #OK259991) in a direct drive inboard water ski boat. Early this season it began to have an issue sustaining high RPM's, it would reach 4800 RPM's with a wide open throttle ( as it should) but then after several seconds it would begin to lose RPM's until it got down to 4000 RPM's, it would then maintain that engine speed but never gain RPM's , all while the throttle remains wide open. I concluded that the engine wasn't getting enough fuel, so heres what I did: Had the carb rebuilt (professionally), replaced all of the fuel lines, new antisyphon valve, new fuel filter, and new fuel pump. None of those things helped at all, the boat runs the same as it did before all that. So, now I think that I may have an ignition problem. So far I have replaced the distributor cap, rotor, and ignition sensor. None of these parts have helped either, the boat is still doing the exact same thing. The spark plugs and wires are about 2 1/2 yrs old. I'm at my wit's end, any help or advice that anyone can provide would be greatly appreciated. Thanks

Re: Mercruiser 350 Mag ignition problem?

have some one push and hold throttle fully open, (while engines off)
could the linkage be slipping or has. do the butterflies show WOT?
rob

Re: Mercruiser 350 Mag ignition problem?

Thanks for the reply, I have checked the linkage and it does appear to be functioning properly and getting to the proper position. Could the coil be the culprit?

Re: Mercruiser 350 Mag ignition problem?

coils have always been a works or doesnt thing to me BUT, I have heard of them getting intermittent if they over heat?
rob

Re: Mercruiser 350 Mag ignition problem?

Like you, I too have heard that coils either work or don't, and I hate to keep replacing parts. Do you know if or how a coil can be tested?

Any other theories on what may be causing this?