cause of dieseling when motor is shut off

[1986cj7]

I have a 1984 AMC 258 i6 / 4.2l carter bbd carb the motor was out of time and the adjustment on the carb was way out I've gotten the timing back to where it should be between 9-12 at 1700 rpms is that correct? Its been awhile since I did my other Jeep. Also has all the emissions stuff on and it is working and idling nice once warmed up. What should I try an octane booster first? It doesn't do it all the time so not sure what else it could be.

 

[Torxhead]

I think that timing is a bit advanced, try about 6 degrees. Is it pinging at all, that would be a sign of too hot of a spark plug. Look down the throat of the carb for any gas dripping also.

 

[Lumpy Grits]

Did you disco the 10"/4" vac. plug wiring?
Ignition and Timing

Best way to stop your issue if the timing is correct, is to burn prem fuel.
Only some dang 'engineer' could come up with the timing procedure for the late model Jeeps.
LG

 

[mtnwhlr]

Is your idle high when it does it?

 

[1986cj7]

Did you disco the 10"/4" vac. plug wiring?
Ignition and Timing

Best way to stop your issue if the timing is correct, is to burn prem fuel.
Only some dang 'engineer' could come up with the timing procedure for the late model Jeeps.
LG

Thanks Lumpy I did forget to disco the vaccum hose from the distributor before checking timing that would help. Thanks for the link also. Looks like also the switches in the link also have to be disco also first time messing with all the emissions control still on these old jeeps.

 

[Lumpy Grits]

That is correct.
Double check your timing setting, after you tighten the dizzy clamp bolt down.
I put white paint on the crankshaft's mark and on the degree scale where I want the two to align.
LG

 

[1986cj7]

Seems like that helped it didn't diesel this time when shutting off. The next couple of days will tell if it is completed thanks again Lumpy.

 

[Hedgehog]

Did you really mean it's between 9*-12* @ 1700rpm? Disconnecting and plugging the vacuum line will help, but timing should be set with the idle set @ ~700rpm. BEFORE the mechanical advance kicks in.

Also, dieseling is usually related to high compression caused by carbon build-up on the cylinder heads.

 

[Lumpy Grits]

Did you really mean it's between 9*-12* @ 1700rpm? Disconnecting and plugging the vacuum line will help, but timing should be set with the idle set @ ~700rpm. BEFORE the mechanical advance kicks in.

Also, dieseling is usually related to high compression caused by carbon build-up on the cylinder heads.

HH-Our late model CJ's have a factory prescribed bull procedure to set the timing.
Check the link I posted.......
Only vehicle I have have ever had, that you had to set the timing like that.
LG

 

[Lumpy Grits]

Seems like that helped it didn't diesel this time when shutting off. The next couple of days will tell if it is completed thanks again Lumpy.

I would still suggest you run premium gas as it contains less ethanol in it than regular does.
LG

 

[Hedgehog]

Seems illogical and crazy to me..... but if Lumpy says its accurate....

 

[1986cj7]

Did you really mean it's between 9*-12* @ 1700rpm? Disconnecting and plugging the vacuum line will help, but timing should be set with the idle set @ ~700rpm. BEFORE the mechanical advance kicks in.

Also, dieseling is usually related to high compression caused by carbon build-up on the cylinder heads.

Yeah but I did forget to disco the vacuum advance hose to dizzy and also this was the first Jeep I've messed with that has all the emissions stuff still on and working I was off on rpms though it should be 1600 rpm been a few years since I have done it.

 

[1986cj7]

So far the dieseling has quit. Thank you everyone for your help.