Mercruiser 4.3l 1991 timing,&mid throtle backfire

[Monte Cryts]

Hello! I have a 1991 bayliner. I put a 1992 chev. truck motor in to get me through the summer while I rebuild the mercruiser. The trouble I am having is the engine runs and idles great. Takeoff has excelent performance, top end is perfect but when I back down to mid throttle it goes to sputering. I changed out all the gas. No change. Changed plug and wires,no change. Changed timming to 4,6,8,10&12 deg.BTDC @ 1000rpm,the only change I seemed to have was the top end began having a sputering at 12 deg. I need to know what the timming should be and at what rpm to set it at, also what the problem could be. Thanks for your time.

 

[akriverrat]

Re: Mercruiser 4.3l 1991 timing,&mid throtle backfire

did you transfer all marine ignition protected parts to new engine...alt,starter,distributor. and carb and fuel pump?

 

[Monte Cryts]

Re: Mercruiser 4.3l 1991 timing,&mid throtle backfire

Yes. I changed the timing chain and gears too. <br />Thanks for asking.

 

[Monte Cryts]

Re: Mercruiser 4.3l 1991 timing,&mid throtle backfire

Opps, I forgot. The truck motor was fuel injected so I had to change to a electric fuel pump.

 

[akriverrat]

Re: Mercruiser 4.3l 1991 timing,&mid throtle backfire

well, my one idea had to do with the auto distributor. so now my head is empty. hear the echo?

 

[DJP]

Re: Mercruiser 4.3l 1991 timing,&mid throtle backfire

Have you blocked the EGR openings on the intake manifold ? Actually, you would also need to replace the intake manifold gaskets with the non-egr type, so the crossover from head to intake doesn't take place at all.

 

[akriverrat]

Re: Mercruiser 4.3l 1991 timing,&mid throtle backfire

dirty/ plugged transition circuit in carb? may get by problem with it accelerating with extra fuel from accel pump. would show on gradual accel and deccel. cam timing ok after changing gears and chain? plug wires back on in correct order?