5.0 Liter Missing Out

[thomasgrant57]

I have an '03 Sea Ray 200 Sundeck with a 5.0 L merc and bravo one out drive with 260hp. I'm having issues when getting close to wot. Around 4500 rmp the boat starts missing out and sort of lagging. I've had it tuned and new spark plugs and my mechanic says it's normal for it to do this. I don't think it's normal. When I first purchased the boat it would run low 50's no problem, now it's low 40's. Has anyone else had this issue? Anything helps...thanks.

 

[scoflaw]

Cap, plug wires, fuel filters , also? Carbed or EFI?. No that's not normal, to misfire at 4500.

With a 555 ignition you should be able to get a read from a scanner, that might give you a clue.

A compression test, and fuel pressure test might not be a bad idea.

 

[CliffA]

what you are calling a 'misfire' at 4500 RPM may actually be the knock sensor retarding the timing to keep the RPM's down....how old is the fuel?....what grade fuel is it?....you may want to try some high octane gas if you are not already using it to see if the problem gets any better......may want to check your ignition timing as well....

have you checked the anti-siphon valve on the fuel tank?....it could be partially clogged and starving the engine from fuel at higher RPM's...

cliff