[matt123]

Hi, Everyone, im having this issue, when i hit 4500 RPM they start to surge up and down and back fires, I currently, have a 4blade 19pitch prop i hit top speed of 35-37 MPH on GPS this is at 4400RPM. any help would be appreciated, i did change a fuel line today because it was kinked going into carb but that did not solve the problem.

[mikeyt]

Your prop should be fine with that engine / boat and you should get into the low-mid 40's with it. The surging / backfiring is usually due to running lean but it may be time for a carb rebuild.

[matt123]

Hey, Thanks for the input, im gonna try that and ill let you know how it goes.

[GregT]

check your fuel filter also, that could be the cause of running lean if it isn't getting the gas it needs due to junk in the filter.

[Lennie]

I have an 18' Diablo with the 3.0L Mercruiser and i was able to hit 4,500 RPM but now I'm lucky if it hits 4,000, full throttle is sounds like i have the anchor down, engine is struggling. Happened all of a sudden too.