merc 4.3- diesels when it is shut off

[BRENT LOGAN]

I have a Mercruiser 4.3 I/O. I am having problems with the engine dieseling, or not shutting down immediately when you turn of the engine? I was thinking it is either a timing issue or a carb jetting issue because the engine seems to be running too rich. The enigne only has 79 hours on it. If anyone has encountered the problem please advise on the fix.

 

[Bt Doctur]

Re: merc 4.3- diesels when it is shut off

Timing
Hi engine temp
Hi idle speed
Lean mixture
Carbon hot spots on piston tops

 

[Don S]

Re: merc 4.3- diesels when it is shut off

What year is it? Why do you say it seems to be running rich?

The most common reason for marine engines dieseling is either high idle rpms (should be in the 650 rpm range, or shutting it down immediatly after a hard run.
After a run, you should let it idle for a couple of minutes before shutting it off. this allows the excess fuel to burn off and the idle to get down to normal.
Those pulling skiers that turn around fast, get back to the skier and shut the engine off often have the problem.

 

[jkust]

Re: merc 4.3- diesels when it is shut off

You can mask the dieseling depending on which problem you have by going to a higher octane gas. This doesn't fix anything but can stop the symptom. My 4.3 has done this since I got it right after the initial break in period. What worked for me was not shutting the key off instantly and waiting a minute. I also started to use higher octane than 87 gas.

 

[wired1236]

Re: merc 4.3- diesels when it is shut off

You can mask the dieseling depending on which problem you have by going to a higher octane gas. This doesn't fix anything but can stop the symptom. My 4.3 has done this since I got it right after the initial break in period. What worked for me was not shutting the key off instantly and waiting a minute. I also started to use higher octane than 87 gas.

Same here. It's happens almost every time when I don't let her idle a little after running hard or use less than 92oct gas so I always use the 92. (The wife will sometimes forget to let her cool down.) On real hot days, I keep the blower on while running hard. Works great.

Last year I went down to Shasta and had to use the 89 octane gas in the marina. I had to really watch it when running hard and make sure to let it idle after a hard ski run. The 92 really makes a hudge difference for me.

 

[z284u2try]

Re: merc 4.3- diesels when it is shut off

I was tired of burning 93 on a non race application. I stepped to a cooler plug.

 

[jkust]

Re: merc 4.3- diesels when it is shut off

Same here.
Last year I went down to Shasta and had to use the 89 octane gas in the marina. I had to really watch it when running hard and make sure to let it idle after a hard ski run. The 92 really makes a hudge difference for me.

I forgot to use 92 one tank and filled a empty half tank with 87 and it was noticable. This might be a silly question but do the MPI v6's do this too?