Let's see some suggestions on how to STOP an engine from "dieseling" during shutdown.

[Kern Dog]

I can't be the only guy that has tried a few things and has mixed results.
I know the basics. People will say that two things that can lead to engine run on after shutting down are spark plugs with too hot of a heat range and throttle blades that are partially open at idle.
Fair enough. Are there other tricks that have worked for you?
Years back when I bought my Edelbrock aluminum heads, I used the recommended spark plugs. I believe they were a Champion RC12YC. I had dieseling with a 440/493-727 combo and because of that, I went down to a RC9YC plug, three steps colder. It stopped most of the run on but not all of it. I defaulted to shutting it off on gear. I do that now with the manual transmission and I'm tired of that. It is a crutch and it should not be necessary.
Regarding the throttle blades, if I back out the idle set screw, as you'd expect, the idle speed drops lower than I want.
Now I have this combination tuned to run better than it ever has but still get the dreaded run on sometimes. I'm currently running NGK plugs, I don't recall the model number but I'm going to see about going to a colder heat range. If that does not work, I'll look to see if the throttle blades are open much.
What then? I guess I could back out the curb idle screw to close the throttle blades then advance the timing to raise the idle speed, right ?
The camshaft isn't radical, it is a 238/242 @ .050 with under .600 lift on a 112 LSA. Timing is at 18-19 initial. The engine never runs hot so it isn't dieseling due to heat. I had the heads off and cleaned up everything so it isn't from chamber deposits either. I'd like to be able to shut down in neutral and have the mill just go quietly.

 

[kiwigtx]

Four-speed manual car......get down to idle and let the clutch out slowly in 3rd gear with the e-brake engaged and foot on the brake.

 

[493 Mike]

Ma Mopar used throttle stop solenoids. You could adapt one. What is your desired idle speed?
Mike

 

[Bighouse]

Do you get any pinging while driving under load & lower rpm’s?

 

[PurpleBeeper]

I’m with Mike. I think an idle solenoid is all you have left to try

 

[69Bee]

As Mike said, I used a solenoid the was used for the ac to set the idle higher when the AC was turned on. I removed the carb idle screw, and used the solenoid to set the idle speed and when the car is turned off, power is removed from the solenoid and closes the throttle blades completely. Never had any dieseling after that.

 

[Dennis H]

Shut it off in gear like the old days. Has never happened since EFI for me.

 

[68-500]

KD first, I hate to start this but. Do you run manifold or ported vacuum advance? If your ported plug into manifold and adjust idle speed. If that doesn’t work like you said try raising idle timing if it raises rpm keep advancing until no rpm change. Adjust throttle blades. I bet that helps.

 

[toolmanmike]

I can't be the only guy that has tried a few things and has mixed results.
I know the basics. People will say that two things that can lead to engine run on after shutting down are spark plugs with too hot of a heat range and throttle blades that are partially open at idle.
Fair enough. Are there other tricks that have worked for you?
Years back when I bought my Edelbrock aluminum heads, I used the recommended spark plugs. I believe they were a Champion RC12YC. I had dieseling with a 440/493-727 combo and because of that, I went down to a RC9YC plug, three steps colder. It stopped most of the run on but not all of it. I defaulted to shutting it off on gear. I do that now with the manual transmission and I'm tired of that. It is a crutch and it should not be necessary.
Regarding the throttle blades, if I back out the idle set screw, as you'd expect, the idle speed drops lower than I want.
Now I have this combination tuned to run better than it ever has but still get the dreaded run on sometimes. I'm currently running NGK plugs, I don't recall the model number but I'm going to see about going to a colder heat range. If that does not work, I'll look to see if the throttle blades are open much.
What then? I guess I could back out the curb idle screw to close the throttle blades then advance the timing to raise the idle speed, right ?
The camshaft isn't radical, it is a 238/242 @ .050 with under .600 lift on a 112 LSA. Timing is at 18-19 initial. The engine never runs hot so it isn't dieseling due to heat. I had the heads off and cleaned up everything so it isn't from chamber deposits either. I'd like to be able to shut down in neutral and have the mill just go quietly.

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You didn't mention what your curb idle is. Shut it off in drive or reverse. (automatic?)

3 heat ranges colder plugs makes it run like dog crap if it wasn't designed for it. When it idles bad it will idle slower. Dieseling is caused by high idle speed. Fix that and your dieseling will be gone.

 

[pnora]

Ma Mopar used throttle stop solenoids. You could adapt one. What is your desired idle speed?
Mike

Thats what I would do.

 

[Darter6]

Ma Mopar used throttle stop solenoids. You could adapt one. What is your desired idle speed?
Mike

I ran one on my Charger. Tho it was for a Edelbrock carb and used on one it looks like you have a Holley. I'm sure they have a kit too.
One last thing, Check the distributor weights and springs for correct function. Possible..

 

[khryslerkid]

If you dont have a leaky carb, (look inside before shutting it down) drop your timing back.

 

[Doorkicker]

what NGK part # are you running now?

 

[R413]

Quick fox before you open the hoo?

Leave it in gear or let the clutch out in gear while while turing it off.

 

[BSB67]

Four-speed manual car......get down to idle and let the clutch out slowly in 3rd gear with the e-brake engaged and foot on the brake.

This.

Clutch in, foot on the brake, release the clutch and turn off key as it starts to grab. Does instantly.

 

[Kern Dog]

Ma Mopar used throttle stop solenoids. You could adapt one. What is your desired idle speed?
Mike

I have a Demon 850 Vacuum secondary. I set the idle to 800. It idles reasonably smooth but idling lower than that just feels strange.

Do you get any pinging while driving under load & lower rpm’s?

Heck no. This setup runs great on even 89 octane. I'm at 9.8 to 1 with these pistons:

 

[Kern Dog]

Shut it off in gear like the old days. Has never happened since EFI for me.

I have been doing that but I should not have to. It feels like a **crutch*.

KD first, I hate to start this but. Do you run manifold or ported vacuum advance? If your ported plug into manifold and adjust idle speed. If that doesn’t work like you said try raising idle timing if it raises rpm keep advancing until no rpm change. Adjust throttle blades. I bet that helps.

I do run ported vacuum.

 

[threewood]

When you drop the idle to shut the blades, advance the timing to bring rpms back up.

 

[pnora]

I have a Demon 850 Vacuum secondary. I set the idle to 800. It idles reasonably smooth but idling lower than that just feels strange.



Heck no. This setup runs great on even 89m octane.

You also have a/c so the idle has to be increased slightly. I would source a solenoid and bracket. Then you will be able to run the increased idle and have it close the plates when shut off. That should help you.

 

[Kern Dog]

You didn't mention what your curb idle is. Shut it off in drive or reverse. (automatic?)

3 heat ranges colder plugs makes it run like dog crap if it wasn't designed for it. When it idles bad it will idle slower. Dieseling is caused by high idle speed. Fix that and your dieseling will be gone.

The Champions ran fine, good idle, no misfires. It sure ran strong. I switched to the NGKs just to see if I'd see a difference. They were no better or worse as far as I could tell.

what NGK part # are you running now?

These were from 4 years ago when I refreshed the engine. BKR7E ?

REPEAT: These plugs were pulled from this engine FOUR years ago when I tore it down for a rebuild after the camshaft went bad.