backfiring mercruiser

[monterey 225]

I have a 1994 Monterey 225 with a 5.7 mercruiser with alpha 1 outdrive. The engine runs fine at idle and revs up when not in gear but backfires through carb and barely will run when put under load. I can barely get 1800 rpm out of it. I have drained and cleaned the fuel tank, replaced fuel lines, replaced fuel pump and carburetor. Engine has new plugs, wires, coil, cap and rotor and has had a compression test and passed. Please help summer is slipping by.

 

[John3]

Re: backfiring mercruiser

I have a 1994 Monterey 225 with a 5.7 mercruiser with alpha 1 outdrive. The engine runs fine at idle and revs up when not in gear but backfires through carb and barely will run when put under load. I can barely get 1800 rpm out of it. I have drained and cleaned the fuel tank, replaced fuel lines, replaced fuel pump and carburetor. Engine has new plugs, wires, coil, cap and rotor and has had a compression test and passed. Please help summer is slipping by.

Hi, that sounds a lot like how mine was, you might want to look at my post of a few minutes ago "Rocker Arm Stud Pulled out". It seems to me that if a Valve is stuck closed the compression could still test ok.
You might want to remove your Rocker Arm Covers. If a stud did pull out the affected rocker arm will be very loose.