Engine dieseling

[Reverend.floyd.lloyd]

I have a 454 big block with a 4 barrel carburetor, everytime I shut it off after going for a drive, sometimes not even a 10 minute drive,the engine diesels and it's taken as long as just under a minute to stop running,I put seafoam through the carb and adjusted the carb and it still diesels pretty bad when I shut it off,does anyone know how I could fix this?

 

[Bent77]

Several things cause this

engine heat
Too much timing at idle
Low octane or bad gas (seafiam won’t fix)
Carb issues (leaking into intake after shutoff)

 

[Babaganoosh]

What carb do you have? I would look at everything Bent said, he knows his way around carbs.

 

[Reverend.floyd.lloyd]

IS

What carb do you have? I would look at everything Bent said, he knows his way around carbs.

It's an Edelbrock carburetor,I'm not sure if the exact one though

 

[ktmoutfront]

Pull the air cleaner off before you shut it off and watch the fuel going into the primaries. If it is leaking down on shut off, it can keep running. Carbon build up in the cylinders will glow red hot after running and will fire that fuel off. Vacuum pulls the fuel through the carburetor jets. As long as it is spinning enough, it can pull fuel through and the carbon keeps it lit, so it keeps trying to run.

Also, is the carb closing enough? Does it idle at 800 RPM when running normal. If the idle is high because the butterflies are not closing, it will diesel. This can be caused by the idle screw not adjusted, the butterfly shaft being worn out, the butterflies not centered in the bore.

Please tell us it is not an Edelbrock Performer carburetor.

 

[JoshHefnerX]

Is it one of the old q-jet type edelbrocks? The old q-jets had some plugs that were inserted as part of the build and they can leak.

 

[Reverend.floyd.lloyd]

Te idle is pr

Pull the air cleaner off before you shut it off and watch the fuel going into the primaries. If it is leaking down on shut off, it can keep running. Carbon build up in the cylinders will glow red hot after running and will fire that fuel off. Vacuum pulls the fuel through the carburetor jets. As long as it is spinning enough, it can pull fuel through and the carbon keeps it lit, so it keeps trying to run.

Also, is the carb closing enough? Does it idle at 800 RPM when running normal. If the idle is high because the butterflies are not closing, it will diesel. This can be caused by the idle screw not adjusted, the butterfly shaft being worn out, the butterflies not centered in the bore.

Please tell us it is not an Edelbrock Performer carburetor.

The idle is àround 800-1000,I can check more later,I believe it's a performance carb,the guy that had it before me had it fleet maintained so blame the snow plow mechanic in downtown slc

 

[ktmoutfront]

What elevation are you at compared to there?

 

[Reverend.floyd.lloyd]

What elevation are you at compared to there?

I'm only a hundred feet if any change,it's a few minutes away from where I live

 

[Wes Harden]

800 to a 1000 rpm, is high enough to keep the throttle plates cracked.
You can fine tune the idle speed with a balance between timing and air fuel and idle speed adjustments.
Add a degree or 2 advance to timing and then back the idle speed screw off.
Not all engines will like the same idle rpm, mine idles 700ish in park and 550 in gear.

 

[gonefishin]

What heat range spark plug are you running? If they are too hot it could cause it.

 

[imiceman44]

800 to a 1000 rpm, is high enough to keep the throttle plates cracked.
You can fine tune the idle speed with a balance between timing and air fuel and idle speed adjustments.
Add a degree or 2 advance to timing and then back the idle speed screw off.
Not all engines will like the same idle rpm, mine idles 700ish in park and 550 in gear.

He has a 454, it can idle lower than a small block.
I agree 800 - 1000 is too high.
I am not sure seafoam is good enough to clean carbon deposits which do cause this problem but with this high of an idle I would start there.