Dieseling on shutdown
 

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

Dieseling on shutdown
 

"Robert M. Gary" wrote in message
...
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.

Dieseling on shutdown
 

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.

Dieseling on shutdown
 

"Robert M. Gary" wrote in message
...
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

I believe you posted about his problem before and I suggested you might have
deeper problems.

Have you tried premium fuel? Check the timing. Is it raw water cooled or a
closed system? Are you sure it is not overheating? A lean fuel condition
can also cause it.

Pinging can also be caused by high cylinder temps. Boats are a lot noisier
than cars so you don't hear the pinging. Both pinging and dieseling are
indications that fuel is igniting without a spark. You need to sort this
one out because I've seen it cause melted pistons. One way to check that is
to pull the plugs and look for aluminum deposits on the ceramic around the
tip.

Dieseling on shutdown
 

Dieseling (from what I've heard) is usually caused by bits of carbon,
stuck to the plug. These are red hot, and keep re-igniting the
residual gas left in the cylinder. Are the plugs wet when you remove
them? Does the engine " puff " blue when you first start it? Could be
valve seals letting tiny bits of oil into the cylinder.

Dieseling on shutdown
 

wrote in message
...
On Wed, 11 Jun 2008 07:30:43 -0400, "jamesgangnc"
wrote:

"Robert M. Gary" wrote in message
...
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

I believe you posted about his problem before and I suggested you might
have
deeper problems.

Have you tried premium fuel? Check the timing. Is it raw water cooled or
a
closed system? Are you sure it is not overheating? A lean fuel condition
can also cause it.

Pinging can also be caused by high cylinder temps. Boats are a lot
noisier
than cars so you don't hear the pinging. Both pinging and dieseling are
indications that fuel is igniting without a spark. You need to sort this
one out because I've seen it cause melted pistons. One way to check that
is
to pull the plugs and look for aluminum deposits on the ceramic around the
tip.


Can also be caused by excessive carbon buildup, which would get worse
over time. Could also be the wrong spark plugs were installed.


Yes, carbon deposits can also cause it. One old trick to remove carbon is
to slowly pour water in the carb while the engine is running at a couple
thousand rpm. The water scrubs the top of the piston and combustion chamber
as it gets turned into steam. You have to do it slowly though. But I would
check the timing and try premium if he is using regular gas before anything
else.

Dieseling on shutdown
 

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.

Dieseling on shutdown
 

On Jun 11, 10:12*am, wrote:
On Wed, 11 Jun 2008 06:57:34 -0700 (PDT), wrote:
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.

The "snake oils" can be effective at preventing carbon buildup, but
you are correct that they don't do much to remove existing deposits.
The "steam cleaning" method of dripping water down the carb throat
while the engine is running will sometimes help. If it's really badly
carboned up, then yes, tear down is the only way to really fix it. I'd
try the steam first, as its very easy to try, and might solve the
problem. On a little 2-stroke air cooled engine, popping the head off
and removing deposits is quick and no big deal. On engines with
overhead valves, it becomes a bit more complicated.

My guess is that the motor in question may have been run for long
periods at very low speed. That's conducive to carbon buildup.- Hide quoted text -

- Show quoted text -

When my Jeep got close to 300k miles, it still had excellent
compression, but carbon buildup caused it to ping, too much
compression! I ended up pulling the head and cleaning the head and
piston tops, problem solved. While I was in there, I took the head to
the shop and had a valve job done and changed out the timing chain.

Dieseling on shutdown
 

On Jun 11, 10:50*am, wrote:
On Jun 11, 10:12*am, wrote:





On Wed, 11 Jun 2008 06:57:34 -0700 (PDT), wrote:
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.

The "snake oils" can be effective at preventing carbon buildup, but
you are correct that they don't do much to remove existing deposits.
The "steam cleaning" method of dripping water down the carb throat
while the engine is running will sometimes help. If it's really badly
carboned up, then yes, tear down is the only way to really fix it. I'd
try the steam first, as its very easy to try, and might solve the
problem. On a little 2-stroke air cooled engine, popping the head off
and removing deposits is quick and no big deal. On engines with
overhead valves, it becomes a bit more complicated.

My guess is that the motor in question may have been run for long
periods at very low speed. That's conducive to carbon buildup.- Hide quoted text -

- Show quoted text -

When my Jeep got close to 300k miles, it still had excellent
compression, but carbon buildup caused it to ping, too much
compression! I ended up pulling the head and cleaning the head and
piston tops, problem solved. While I was in there, I took the head to
the shop and had a valve job done and changed out the timing chain.- Hide quoted text -

- Show quoted text -

Did you flux it first? I might have if I were doing all that to an
engine with 300 on it.

Dieseling on shutdown
 

On Jun 11, 3:04*am, "Reginald P. Smithers III" "Reggie is Here
wrote:

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.

I wish. I'm pretty well equipped to deal with complex motors. I have a
full function scanner (can send commands, ABS, airbags, all of it) for
modern cars. This is a simple carb and distributor boat, no computer
to tell you what's up.

-Robert