Robert M. Gary wrote:
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

When engines were simple and I played with my engine, dieseling was the
result of improper timing, idle speed set too high, fuel too low in
octane (pinging and dieseling), and/or engine running hot. You had to
play around and by trial and error correct the problem

Today, the engines are so complex, I think all of the engines have
computers on board. If you have a fairly recent vintage, your mechanic
only has to plug them in to a diagnostic tool and it will tell you
exactly what the problem is. The local AutoZone will run the diagnostic
test for free, I am sure other auto supply retailers offer similar
services.