TIMING & RUN-ON

[FJ5 1970 440]

I've got a carbed 440 with the electronic ignition conversion and it likes to run-on. It starts and runs good, i don't have the ability to check or set it properly at this time so I've been retarding timing (turning distributor CC) in micro movements, maybe 6 or 8 degrees so far with no good results. The vacuum advance is connected to the ported side of the carb and I checked that port with a gauge and there is 0 psi at idle. So what gives? Do I need to just keep taking away timing or should I be looking for problems with other parts? Thanks all.....................

 

[70chall440]

Run on can be caused by several things one of which can be timing, however another cause can be heavily carboned up cylinders. During running the abundance of carbon deposits get very hot and act as a spark plug of sorts.

That said I would not be just retarding the timing without knowing how much you are moving it. 6-8 degrees is a fair bit which indicates that it might have been too advanced.

What is the back ground on the engine, is it original to the car, has it been rebuilt, etc.

 

[FJ5 1970 440]

Run on can be caused by several things one of which can be timing, however another cause can be heavily carboned up cylinders. During running the abundance of carbon deposits get very hot and act as a spark plug of sorts.

That said I would not be just retarding the timing without knowing how much you are moving it. 6-8 degrees is a fair bit which indicates that it might have been too advanced.

What is the back ground on the engine, is it original to the car, has it been rebuilt, etc.

The motor is not original and has been rebuilt about 6K miles ago. It's not a wildly built street drag racer, more of a nice driving ice cream getter that performs good. It was running rich and I leaned it out and changed the spark plugs. The old plugs were 8's and indicated a pretty rich condition. I put in 12's and haven't had them out yet for a look see. Any procedure to decarbonise the motor or any other thoughts?
Thanks.......................

 

[Steve340]

Check for the plugs being too hot heat range- stock plugs would usually be OK for a street car.
What is your compression ratio - too high and you will get run on.

 

[FJ5 1970 440]

Check for the plugs being too hot heat range- stock plugs would usually be OK for a street car.
What is your compression ratio - too high and you will get run on.

This car is new to me and I was told it came out of a camper or RV. I'm inclined to believe that and that the heads are also of the same origin. I looked around the web and it seemed like most people were running 11's or 12's. The car also has a 28" radiator and does not run hot. I suspect (or should I say I have a gut feeling) it's something to do with the distributor but don't really have anything to back it up. Wish there was some way to test it........

 

[Ele115]

Get a timing light and start there.

 

[FJ5 1970 440]

Get a timing light and start there.

Yea I know, it's on the list and it will be a while.......................

 

[Righty Tighty]

I recently had a run-on issue with my 440 6BBL. There were many issues going on at the same time (still some issues), but long story short, my timing was too retarded. Initial was at 14, I advanced it to 20, and it's very happy. Idles nice with no run-on after a cruise at operating temp.

Timing lights are cheap and invaluable. They're available used for $10-20 all day long on Craigslist, or you can get a very decent one for $40-50. If you're going to be doing your own tuning, don't even bother until you have a timing light.

 

[FJ5 1970 440]

I recently had a run-on issue with my 440 6BBL. There were many issues going on at the same time (still some issues), but long story short, my timing was too retarded. Initial was at 14, I advanced it to 20, and it's very happy. Idles nice with no run-on after a cruise at operating temp.

Timing lights are cheap and invaluable. They're available used for $10-20 all day long on Craigslist, or you can get a very decent one for $40-50. If you're going to be doing your own tuning, don't even bother until you have a timing light.

OK So I broke down and bought a timing light. It slightly after TDC. It's now about and I mean about 10* before TDC. Got some degree tape on the way. When you rev it up it sure seems to have a lot of total advance. Here's what I'm working with. Still runs on, maybe a little worse.

 

[Ele115]

You could try 5 more degrees. Is the car running hot? Also, check a few plugs again. Double check idle mixture, and hopefully you don't have some ridiculous setting on the idle speed screw. If you can't get it to behave you may want to bring it to the TDC mark on the dampner and pull the cap off the distributor and verify that the rotor is pointing right at one and not way off, but not yet. If the timing is getting you nowhere, the carb or crap fuel could start to look suspect. Has it always done this? I would look at the timing a while longer, advance it a bit more. Long shot, but it the compression is really high, it could need higher octane. I have a couple cars that would definitely diesel if I tried to put pump gas into them. My boat would for sure. That's a long shot though.

To summarize: This is USUALLY timing. It CAN be carburetor issues and fuel quality/octane. Heavy carbon deposits with glowing red hotspots will cause dieseling. Probably in about this order of probability in your case. If it ran super rich for a long time, the carbon build ups may factor in. You could do the old dribble the water down the carb while you rev it trick if you have any concerns

 

[heminut]

Run on can be caused by several things one of which can be timing,

How can timing have any effect on run on once the ignition is shut off?

 

[FJ5 1970 440]

How can timing have any effect on run on once the ignition is shut off?

Good question, I hope someone can explain it because I sure can't. It almost seems to imply some stray voltage is running around.
.

 

[Steve340]

If a "hot spot" is in the combustion chamber it can run on because the hot spot can ignite the fuel after the ignition is switched off.
Timing either retarded or advanced can be one of a few factors that can cause this.
Sometimes it can be a bugger to find the cause and remedy run on.

 

[Chryco Psycho]

Retarded timing can trap more heat in the cylinders as combustion is late & less heat exits through the exhaust .
Run on is usually a combination of idle mixture , idle speed ,, timing , wrong spark plugs , carbon build up , all contributing to enough heat to keep running without spark .

 

[Adam]

I've got a carbed 440 with the electronic ignition conversion and it likes to run-on. It starts and runs good, i don't have the ability to check or set it properly at this time so I've been retarding timing (turning distributor CC) in micro movements, maybe 6 or 8 degrees so far with no good results. The vacuum advance is connected to the ported side of the carb and I checked that port with a gauge and there is 0 psi at idle. So what gives? Do I need to just keep taking away timing or should I be looking for problems with other parts? Thanks all.....................

I had an old Bronco that used to do that... it was the carb. Try turning the idle mixture screws out (richer) and then lowering the idle/rpm screw. The extra richness is needed to keep the engine running at a low rpm. Counterintuitive, but it works.

 

[fasjac]

And could be unburned fuel in the intake when you kill the ignition. All above for sure. I’d think timing and carb adjustment first.

 

[Don Hagen]

One more thing to look for is a vacuum leak at the intake or carbs. I had the same issue on my 63 Galaxie a couple years ago and finally nailed it down to a vacuum leak at the back of the intake. Big block Mopars obviously have a different intake design than a BB Ford but it may be leaking air around the carb base or somewhere on the carbs.

 

[FJ5 1970 440]

One more thing to look for is a vacuum leak at the intake or carbs. I had the same issue on my 63 Galaxie a couple years ago and finally nailed it down to a vacuum leak at the back of the intake. Big block Mopars obviously have a different intake design than a BB Ford but it may be leaking air around the carb base or somewhere on the carbs.

Didn't consider that, thanks D .........

 

[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

 

[heminut]

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

Exactly!