Engine run on/dieseling

[picard767]

I have a 472 hemi ( stroked 426) with dual ( Edelbrock ) 4bbl carbs with no manual or electric choke. Mopar Performance (orange box) electronic ignition. 10.5:1 pistons.
Any advice on best way to prevent dieseling would be greatly appreciated.

 

[63RedFury]

My Dads Hemi did the same thing.We reset the timing and put in different spark plugs (hot I think it was) and that took care of it.

 

[Pops1967GTX]

First are running a high enough octane fuel? Check that the throttle blades are not open too much.Try adjusting the idle speed down a bit or a possible vacuum leak .

http://www.thecarburetorshop.com/Troubleshooting.htm

 

[super-bee_ski]

I'd start with fuel octane rating and Ignition timing...
Dieseling could be a symptom (one of many) of items OR as you know cuz your smarter than me...a combination of items.

 

[66Satellite_in_NC]

Is this a problem after a new build or is this something that it just started doing after running properly? If the later, you might have some carbon that is staying hot inside a cylinder or multiple cylinders firing the fuel. I would try some seafoam before anything and see if that helps. I have also heard of old racers using water, but not enough to hydro-lock it, to scavenge out the carbon.

 

[picard767]

Thanks Pops1967GTX. I am using 93 octane. Agree on the idle; I raised it so it wouldn't stall while cold. I'll take it back to 700-750 warm.

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63683GTS - thanks for the reply. I will try a colder plug and adjust the timing a bit. Appreciate the info.

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Thanks for the info super-bee_ski. Looks like a combination of a/f mixture, timing, colder plugs, warm idle speed. I guess I'll do the dance until it's fixed.

 

[Grabinov911]

I'm all over this thread. Same problem, on a brand new build. Stroked 440/493. 10.5 to 1 w Edlebrock heads and aluminum pistons. Engine diesels when shut off if it's warm. Doesn't do at all when cold. Running 91 octane cause it's all I can get in CA.

I've been shutting the engine off with the car in gear (727 auto with a pretty loose 9.5" Dynamic torque converter) and even that little amount of drag is enough to keep it from happening. If that's indicative of anything.

Hey 66Satellite: You asked Picard whether a new build or not. Since mine IS new, i'm guessing no carbon issues, so what's the alternative? Gonna check timing and vacuum for possible leaks. Which way would I go with plugs to try that? Hotter or Colder?

Thanks

 

[picard767]

Thanks 66Satellite_in_NC. It's a year old build and has been doing it since the beginning. I'm going to redo a/f mixture, warm idle, timing, and plug type. Looked up SeaFoam and watched some youtubes on it. Thanks.

 

[bigblock]

If aluminum heads try a colder plug. If the CR is too high then try High octane or race fuel. Also a high throttle valve angle will cause this. If so idle it down or rig up a solenoid to close the throttle completely when switched off.