1987 165 hp 4 cyl mercruiser - back firing

[DVLWMN]

When you are accelerating the engine back fires through the carburator. The engine will run rough at low rpm's. We have rebuilt the carb and put on a new timing chain. These didn't seem to solve the problem. Can it be in the ignition? What do you suggest?

 

[searay3]

Re: 1987 165 hp 4 cyl mercruiser - back firing

Can you post the serial number for your engine? Did you run a compression check to make sure there are no valve/cyl issues? When was the last complete tune-up?Carbon tracks in the distrib cap can cause mifiring/backfiring. As far as backfiring goes, that can be timing or a lean condition. Why did you change the timing chain and what else was removed/ repaired at the time. The reason I ask, is something like an intake manifold leak could be an issue. Double check the firing order and the rotor is pointing at #1 plug when at tdc. Remember, the damper has to turn 2 revs for a complete cycle, so it is feasible the distrib is in 180 off. .

 

[Almeja]

Re: 1987 165 hp 4 cyl mercruiser - back firing

Check your engine vacuum... IMHO it sounds like it could be a bad/sticking intake valve.

I guess you might toss in an electrical tuneup first as it is quick and cheap. Check/clean/replace points, condensor, rotor, cap, plug wires, timing, advance mechanism.

I've not heard of a 165 hp 4 cylinder Mercruiser... all the 4 cyl models I've seen were rated between 130 and 140 hp. The 6 cylinder in-line chevy engine models are rated at 165 hp.

 

[Don S]

Re: 1987 165 hp 4 cyl mercruiser - back firing

Sure an ignition system can cause your problem. Do a full tuneup, including a compression test, set the dwell, then the timing, also check the plug wires.
You may also have a cracked coil tower which would cause a misfire.

Almeja:
The 165 he is talking about is the Mercruiser 470 style 3.7L engine, the 130-140 hp models you are thinking about are the Chevy 3.0L engine