engine run on cause?

[ltrripp11]

gentleman

whats usually the cause of engine run on when shutting the car off? its happened a couple times recently when hot. i suspect a timing issue and if so is it indicitive of to much advance or to retarded? thanks.

 

[daredevil]

Generally too much advance. Other causes are too low of an octane,too hot of plugs, hot spots in the combustion chamber or a leaky carburetor

 

[mtna_buzz]

Try lowering your idle speed a little. Ignition timing shouldn't do it - no spark when the key is turned off.

 

[RedFish]

I second Idle rpm too high.

 

[mullinax95]

If you have a manual trans let the clutch out a little to slow the RPM down and then shut if off. It works trust me.

 

[66plyValiant]

idle is set too high,try idling it down before spending money on spark plugs. idle RPM should be 750-800 rpm depending on if its stock or not, if modified idle it down to where it idles without shutting off

 

[crackedback]

Not enough initial timing causing throttle blades to be too far open at idle.

 

[dodge freak]

I can make any engine with a carb run on, just press on the gas pedal and shut the engine off.

The throttle is open too far, why ? crackedback might have it

 

[RedFish]

Many of the early import carbs on 4 banger engines had a solenoid to push the throttle wide open at switch off.Anti backfire and anti run on solenoids.

 

[67Dart273]

Not enough initial timing causing throttle blades to be too far open at idle.

Plus smog motors with retarded timing run hotter "promote" dieseling

 

[omahamoparguy]

Hot spots in the combustion chamber combined with air source whether it be throttle open too wide (high idle) or loose throttle shafts letting air in. Now all yu need is some fuel AND the fuel will keep flowing with a carb as long as there is vacuum. so, you got to get rid of one of the things. The best would be to rid the chamber of various hot spots caused by carbon deposits and or sharp edged. Old VW air cooled's had a fuel shut off solenoid (Solex 34 PICT carb). I had this problem on an old slant in a 64 dart. I did the old mechanic trick by running water through the carb whilst the engine was running (hand throttling it). One thing that helped; I noticed that the throlle linkage was hanging up sometimes and not letting the throttle plates close all the way. By fixing this it helped more than anything. Make sure that the throttle linkage is not hanging up at all and you got a good return spring. (too long of an answer I know!)