dieseling 4.3 merc.

[Strick]

I have a 1994 28' larson with twin 4.3 LX alpha's with about 420 hours. Every once in a while (once every 10 times +/-) the engines will diesel & knock for a while then the iginition is shut off. What gives???

 

[Don S]

Re: dieseling 4.3 merc.

The 2 main reasons are to high an idle rpm (needs to be 700 or below.<br />Or shutting the engine off immediatly after a run without a chance to cool down a bit. Just let it idle for a minute or so and it should shut off fine.<br />Then you get into needing a tuneup, timing off, advance timing off or sticking, mixture on carb off. Too low an octane rating (NOT a common problem as 87 should work fine.)

 

[Dunaruna]

Re: dieseling 4.3 merc.

Originally posted by Don S:<br /> Too low an octane rating (NOT a common problem as 87 should work fine.)

Agreed - not common, but out of date fuel may not be 87. Out of date fuel is common.

 

[Strick]

Re: dieseling 4.3 merc.

Originally posted by Don S:<br /> The 2 main reasons are to high an idle rpm (needs to be 700 or below.<br />Or shutting the engine off immediatly after a run without a chance to cool down a bit. Just let it idle for a minute or so and it should shut off fine.<br />Then you get into needing a tuneup, timing off, advance timing off or sticking, mixture on carb off. Too low an octane rating (NOT a common problem as 87 should work fine.)

Bet it is the second one- Ususally has happened after running for a bit. I'll let it mellow for a while before killing it from now on. Thanks.