engine run on

[CONMAN]

I'm not very engine savy and have a problem where the engine runs on a few seconds after being shut down. Is that plugs or timing? Would like some input so I can get it looked at by local shop.
Thanks

[ken swart]

First time out this season it happened to me. Even though I used Stabil I think last fall's gas lost something. I added 1/2 tank of 100 octane and that stopped it. My engine normally runs fine on 93 octane.

[vector1]

too much compression or not enough octane would be my guess. turn the idle down if possible will help also.

[native1]

Make sure plugs are clean. Carbon deposits can glow and cause run on. Also can check timing, and idle/air mixture on carb. Don't run it too fat on the mixture. I had the same problem and this helped me. But when its hot it will sometimes do it anyway. I am always ready to pop the clutch during shut down to stop the engine over run. I hear it is bad for the valve train to run on so try not to let it happen. Of course 100 octane always helps. Good luck.

[Excaliber]

It's low octane for the compression all right. It MIGHT clear up if you drive it awhile and flush out the old gas and go with new. If it persists higher octane fuel will usually stop it. What I do is simply leave it in first gear, ease out the clutch until I feel the car wants to move, turn off the key and finish letting out the clutch with my foot on the brake. Deiseling is really bad for your motor, whatever you do, STOP IT from happening, NOW.

[RodKnock]

Do you have an MSD? If so, a "run on" condition is addressed in their manual. Bottom line, a diode must be installed within the wiring, but I'm no expert.

[vettestr]

Conman,
As mentioned several thing can cause run-on. High idle speed can cause it so check your RPM and reduce it higher than normal for your engine. 750 to 850 RPM is a ballpark but this depends on what's in your engine. Sticking float levels are another possible but other symptoms would be present. Badly carboned plugs or combustion chambers can cause run-on so maybe your meck a nick who can see and hear it run would be your best bet.

You can stop the engine run-on by holding your brake down and releasing the clutch with a little finesse and her in high gear.

[Eljaro]

I did have run-on all the time with my 427BB, no matter what I did. I had a Holley 850CFM mechanical pump four barrel and did everything you can think of and never got rid of run-on.
I have Webers now and do not know what run-on is. Maybe it has something to do with the carburetor, because everything else is unchanged.
But I think that it could have to do with the advance of the ignition, because with the Webers I did have to advance ignition to 18º. I never did that when I had the Holleys on, and maybe doing that could help. Retarded ignition will heat up engine more and that could cause run-on.

[Double Venom]

Conman,
If I may, assuming your engine is set up right, IF you are running an electric fan, ESPECIALY DUAL FANS, they act lilke small generators and will feed 12v's back down the system especailly with an MSD box and will allow the enrine to run on until the fan(s) slow down enough to drop voltage. If this is the car this is where you would put the diode in, the feed lines to the fan (s). Very common problem with week grounds in these cars.
DV

[wtm442]

Originally Posted by Excaliber

Dieseling is really bad for your motor, whatever you do, STOP IT from happening, NOW.

Dieseling can damage the motor. Many cars in the old days (~65 to ~85) had a anti-dieseling solenoid. It was an electric device that acted as a throttle stop. When energized, it positioned the throttle at its proper place, but when the key was turned off, the throttle was allowed to close even more to eliminate the run-on. Try higher octane gas and make sure your initial timing is correct. If that does not cure the problem, its time to search thru some junk yards for the solenoid and bracket from a car with your motor.

http://www.autozone.com/az/cds/en_us...rInfoPages.htm

Just anther thought to add to the list.

[CONMAN]

Thanks for all the replys. I have just replaced the plugs and am using the highest octane available so I'll try getting the timing checked. Again, thanks.

[blykins]

What's it idle at?

[Excaliber]

I have to run a high idle rpm (1000-1100) on my engine, well, I don't 'have to' but I like it up there. If I run 'race gas' it shuts off fine, but that's a hassle and expensive, so I just run premium gasoline from the pump and 'deal with' the run on by using the clutch to kill the motor.

With a high idle speed after shut down by the key, the motor continues to pull air/fuel through the carb(s). This fuel/air is then detonated simply from engine compression/heat and/or glowing embers in the combustion chamber, which will ALWAYS be there no matter what you do. Self detonation is effectively 'deiseling'. Lower octane fuel ignites more readily than higher octane fuel, which is why the higher octane fuel resists self ignition and usually stops engine run on (deiseling).

Lower engine rpm idling, in my case, tends to foul the plugs if it is prolonged (long red light) and can cause a miss fire when I accelerate as the plugs clean themselves off. Thus, I prefer a higher idle rpm to avoid the hassle of a miss fire. An occasional blip of the throttle also works to clear the plugs, but what ever... Higher idle speed and a clutch kill works for me.

[CONMAN]

It idles at 1000 rpm

[blykins]

Is the cam big enough to need that high of an idle? Have you tried to idle it down to around 800? That would be a very easy thing to try and it may help your problem.

Do you know if it's a solid roller camshaft?

[CONMAN]

yes it is a solid roller cam

[dlang14]

Originally Posted by Excaliber

What I do is simply leave it in first gear, ease out the clutch until I feel the car wants to move, turn off the key and finish letting out the clutch with my foot on the brake.

I'd humbly suggest 3rd or 4th gear. Last thing you want is to get it wrong and hit the garage wall in front of you

[wtm442]

Originally Posted by dlang14

I'd humbly suggest 3rd or 4th gear. Last thing you want is to get it wrong and hit the garage wall in front of you

I back the car in the garage and leave the door open any time I start it or turn it off.

[patrickt]

Didn't we have a thread recently about a fella that drove his Cobra through the front of his garage?

[blykins]

Well, I was going to recommend that you idle it down, but since it's a solid roller, IMO it's best to keep it idled up. Glad I asked. Even with the pressure fed lifters, it's nice to have more oil splash to help with longevity.

I'd try some timing changes.