On Jun 11, 5:45*am, "Jim" wrote:
"Robert M. Gary" wrote in ...

I have a Bayliner with a 4.9L 190 hp carb'd Merc engine. When I shut
down it diesels for awhile. The dealer says that the longer I let it
idle first the less it will do this but the issue seems to be getting
worse. The engine isn't running hot and the water impeller was
replaced about 8 months ago.
I've done a lot of car work but its been a long time since I've worked
on a carb'd & distributor car. I seem to remember that dieseling is
caused by high cylinder temps. I thought you could affect it with
timing but I might be thinking pinging. What should I be looking at
for my dieseling issue?

-Robert

Set your timing and idle speed and mixture. Clean spark plugs. De-carbon
engine. Let idle a minute or two before shutting down.

There's been many, many tests on the snake oils they sell to decarbon
an engine. In summary, the only way to do it is tear it down.