4.3L mercruiser dieseling

[Tafflad]

I have a 1 yr old Maxum, with 4.3L carb Mercruiser.
Using standard 95 RON fuel

It has done 32hrs.
I have found that it frequently runs on when switched off ... sometimes for up to 20 sec. or more.
This is not on particulary hot days ... but it happens on them as well.

Boat is not being driven hard, and everything is as standard - incl the platinum plugs.

A bit of Googling - has found :
99% chance of it being Throttle butterfly not closing
Cooler running thermostat needed
Cooler plugs needed
99% chance Bad fuel
Idle speed too high
Mixture too rich
99% chance timing is out


Be interested to know where would be best place to start ?

Or as under warranty ... is this a warranty item, and I should just book it in ?

 

[JustJason]

Re: 4.3L mercruiser dieseling

iridium plugs in a carb'd boat motor????

anyways.... what's your idle rpm??

if it's only 1 year old don't cha have any kind of warranty on the motor??? take it back to the dealer.

 

[Don S]

Re: 4.3L mercruiser dieseling

The most common 2 reasons for dieleling are
1. Idle rpm too high
2. Immediatly shutting off the engine after a run, without a cool down.

The first one is easy, just set the idle down to 650 to 700 where it belongs., the second, when you come off a run, let it idle for a couple of minutes before you shut it down.
DO NOT allow it to diesel for 20 seconds. This can pull water in from the exhaust, hydrolock the engine and cost you an engine.

Here is the merc service bulleten addressing the problem.

http://www.4shared.com/account/file/53242775/d72d01/Engine_Dieseling_or_Running_on.html

PS: Cooler plugs are seldom needed.