4.3L carb Mercruiser dieseling

[Argonaut]

Had a good day out today on my 2007 1800SR3.
Noticed on several occasions, when you switched off - the engine would run on (dieseling)
The engine has only done 30 Hrs ... so no carbon build up, and it was not being worked hard ... 22mph kneeboarding.

The engine is all as standard - and has the platinum (high cost long life spark plugs)

Any suggestions .... or is it just a case of putting in under warranty.

[Brit Rider]

These engines are famous for this, mine did it back in 2003 and I'm not aware of a fix, even though Mercruiser reckon they have - its gotten better but is by no means resolved.

It diesels because of the high temp reached in the combustion chamber - only way I ever found to stop it was, after a long run or toy-towing, to let the engine idle for a bit before shutting it down.

We tried everything, different plugs, changing the timing slightly, fuel additives, cooler thermostat to name a few and nothing ever fixed it properly.

The only answer I ever got from my dealer was "Its American, what did you expect?!"

[seapuppy]

"Its American, what did you expect?!"

HEY!!!..that was a cheap shot!!....hahaha....it's true...but hey!!..


yep...he's right...let it idle a bit...try adjusting the idle jets down just a touch.....

that's about all that can be done!!..


SP

[Brit Rider]

I didn't say it... It is somewhat infuriating though to see Mercruiser still not addressing these issues when other (American! ) power plants like PCM and Indmar go from strength to strength...

[Argonaut]

There is a Mercruiser Tech note on this Happy to post it, but don't know how to add this to this forum.
... they list a whole number of things ...


Idle speed too high
Timing wrong
Mix too weak
Poor fuel
Plugs - fit cooler grade
Carb butterfly valve not closing at idle


As engine had only done 30 hours .. .and none since service - took it back to service shop ... Celtic Marine, and was told .... idle is too high (1000rpm instead of 600) timing was 5 degree out.

They set it correct and when I asked how come it was so far out as they had done a full service ? ..... they added they would not check idle & timing on a service !

Wonder when they do check it?