Run on

[oneof52]

Hello, need a little help. 70 Cuda 440-6 all carbs have been professionally rebuilt. The problem I am having is that on occasion, when I shut off the car, continues for about a second or two, then stops. Does not happen all the time but about 30% of the time. Timing is at 4 degrees BTC and engine runs fine. Most of the time the engine will shut off normally. Any suggestions would be appreciated. Thank you

 

[Challenger RTA]

Dieseling or engine run-on is a condition that can occur in spark-plug-ignited, gasoline powered internal combustion engines, whereby the engine keeps running for a short period after being turned off, due to the engine kicking back upon shutdown, drawing fuel through the carburetor, into the engine and igniting it without a spark. That's Dieseling

 

[oneof52]

Thank you for the definition, how do I fix it ?

 

[Challenger RTA]

Octane or timing. Change plugs heat. Carbon on valves.

 

[Challenger RTA]

This can be caused by a number of things:

1) Too fast an idle speed.

2) Too rich fuel mixture. (Long-term causing carbon build up which glows hot and ignites fuel after the ignition circuit has switched off)

3) Too lean a fuel mixture at top end from incorrect jetting or airleak, casuing the engine to overheat.

The fuel/air mixture could be heated to the point that it self-ignites, causing the diesel run-on effect.

4) Timing is out. The timing itself won’t cause the run on as the ignition is switched off when the run in occurs. However timing too far advanced can cause an overheating engine which can attribute to over-run.

5) Lower octane fuel could aggravate the problem, because it will self-ignite quicker than a higher octane fuel. But it alone won’t cause the problem.

6) If you run a single or twin carb setup that has electromagnetic idle air cutoffs (usually solex only) it is meant to also keep this from happening by cutting off the idle air circuit when the ignition switch is turned off. Check these are working.

7) Sparkplugs have a temperature range. Are you running the right ones for your engine spec? Also are they clean and gapped correctly?
As with any running issue I always advise to make any adjustments logically. 1) Valves 2) Timing and ignition system check (point and plug gap and clean) 3) Adjust carburetor / inspect fuel system.

 

[oneof52]

Thank you everyone, here are my specs: 440 .030 freshly rebuilt, 904 heads, 10.1:1 compression, new valves , new mild cam , E3 plugs, freshly rebuilt carbs. Cold rpm at 1000, warmed up at 750 at warmed up with 4 degrees BTC.
I will adjust the fast idle with the tab and curb idle with the solenoid to 950, and the screw on the carb to 650. Running 91 octane with lead additive

Given that it is a freshly rebuilt engine, is the 4 degrees BTC correct even close?

Keeping in mind, dieseling does not happen all the time

Thanks in advance

 

[Adam]

Often times it is caused by too lean of an idle screw adjustment. I know this sounds contradictory but what happens is guy will turn the idle screw in to lean up the idle mixture and also turn in the idle adjustment screw to raise the idle, this can cause some gas to be pulled from the Venturi. When this occurs the engine will try to run on, when shut off.

Try this, richen up the mixture screw and as the engine increases in rpm turn out the idle adjustment screw (by the linkage), lowering the rpm. Adjust it to idle at your desired rpm, making sure the butterfly is closed, and only the idle circuit is running the engine, as much as possible.

 

[Chryco Psycho]

It should run a lot better around 14* BTC assuming you have no ping

 

[Ricks72Chlgr440]

4 degrees before is too retarded. Like Chryco said, running more timing will wake that engine up, make it run cooler, and likely vastly reduce the dieseling issue you're having. Advancing your timing will require you to reduce your idle speed and may require you to readjust your idle mixture screws. Take your time with this and the engine will be much happier.

If you would please, make these changes and report back here your results. This will also help others with similar issues.

 

[Old Mopar]

Professionally rebuilt does not include professionally tuned. This fuel system requires a specific baseline set up once installed on the car - unless this is followed the car will never run properly. There are specific tools required as well. There is not a simple answer to your situation as there are too many unknowns

 

[oneof52]

4 degrees before is too retarded. Like Chryco said, running more timing will wake that engine up, make it run cooler, and likely vastly reduce the dieseling issue you're having. Advancing your timing will require you to reduce your idle speed and may require you to readjust your idle mixture screws. Take your time with this and the engine will be much happier.

If you would please, make these changes and report back here your results. This will also help others with similar issues.

Thank you, much appreciated. Will revert with updates

 

[Vinny]

Do you have anti dieseling solenoid present, hooked up and properly set up? My A12 never runs on and I've owned it since 1989.

 

[oneof52]

Thanks, but have not heard of Anti-Dieseling solenoid - do you have a picture?

 

[Challenger RTA]

Even though these are commonly known as an "idle solenoid", they are correctly referred to as an "anti dieseling solenoid" or "idle stop solenoid". Their purpose is not to raise the idle, but to close the carburetor throttle completely when the key is released and prevent engine run on. The reason they came into being is from all of the emissions equipment, heavy loads like A/C compressors, high output alternators that all require a higher idle speed to stay running. That idle was so high that something was needed to allow the carburetor's butterflies to close completely thereby eliminating engine run on. They were never designed to push the carburetor open on their own. Only to hold it in place until the key was turned off.

 

[oneof52]

Thank you for the details, I know the “idle solenoid” term, but your description makes sense. There are a few adjustments I need to make (once the weather warms up in NY). On my car, all I have is a PS pump and Alternator.

 

[Vinny]

Even though these are commonly known as an "idle solenoid", they are correctly referred to as an "anti dieseling solenoid" or "idle stop solenoid". Their purpose is not to raise the idle, but to close the carburetor throttle completely when the key is released and prevent engine run on. The reason they came into being is from all of the emissions equipment, heavy loads like A/C compressors, high output alternators that all require a higher idle speed to stay running. That idle was so high that something was needed to allow the carburetor's butterflies to close completely thereby eliminating engine run on. They were never designed to push the carburetor open on their own. Only to hold it in place until the key was turned off.

Great explanation. I appreciate you helping to clarify. Pictures are all over the internet.

 

[Vinny]

Here's my factory set up. Zoom to the right of the center carb, between the linkage and the spring. There you will find the solenoid that will cure your run on condition. Good luck.

 

[6PKRTSE]

It's the E3 spark plugs. They make so much extra power according to the commercial that it just wants to keep going even after shut off.... lol. Had to... As mentioned, more than likely timing.
I have brand X buddies that just shut their vehicles off in gear and then put it up in park. They claim because of how big their camshafts are that cause their dieseling. Lol. Then I tell them that I have a .815 lift in my street car and it does not diesel when I shut mine off???

 

[fasjac]

All good responses, if you have adjusted your idle speed with the outboard carbs connected, you may have the blade’s slightly open when you kill ignition.
Always adjust the center carb with the outboard carb linkage disconnected.
Simply reconnect the outboards when your finished adjusting.
I made that error many years ago, and it will cause the run-on as well.

 

[oneof52]

I shave a lot to do this weekend. Much appreciate everyone’s help. I will report back early next week