mrhollywood
Well-Known Member
My car sometimes wants to "run" after I turn the key off. What causes this?
Carb Question
- Thread starter mrhollywood
- Start date
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65Val
Average Length Member
Unless you have the idle set way too high, its probably not the carb. Run-on or "dieselling" is usually caused by excess carbon buildup glowing in the combustion chambers , so when you turn off the ignition, these glowing bits will act like a spark and fire the excess fuel in the chambers, causeing the run-on.
To de-carbon the engine, you can use that SeaFoam stuff, or, ("CheapSkateWay"©)TRICKLE some water down the carb while revving the "p*ss" out of the engine, in Park/neutral, of course. The water turns to steam and really cleans out the excess carbon.
To de-carbon the engine, you can use that SeaFoam stuff, or, ("CheapSkateWay"©)TRICKLE some water down the carb while revving the "p*ss" out of the engine, in Park/neutral, of course. The water turns to steam and really cleans out the excess carbon.
cudajim
cudajim
I always thought it was caused by a spark that's too advanced combined with too fast an idle.
65Val
Average Length Member
Yes. You may have noticed I mentioned too-fast of an idle as one of the causes, but advanced timing has nothing to do with it.
green1
Well-Known Member
Idle too high, advance has nothing to do with it. Re -tarded can. adjust the carb. To idle at 750 or less.
cudamark
Well-Known Member
X2.......decarbonizing helps too.....
6pakattack
Well-Known Member
Good ole Marvel Mystery Oil,or Sea Foam !!
slantsixdan
=..=
You've had some justifiable guesses so far, but run-on (or "dieseling") has many causes -- yes, including improper idle adjustment and overly-advanced timing, among others -- so in order to help you narrow in on what's causing it in your car, we need more info. What's your basic timing set at? What spark plugs are you running? What's your engine idle speed? Any modifications or recent work done on your car? Is yours a California-emissions car, originally?
You may not know the answers to some of these questions, so to avoid wasted time, tune-up parts and technique suggestions in this thread. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. And you'll want to get the three books described in this thread as soon as you can.
You may not know the answers to some of these questions, so to avoid wasted time, tune-up parts and technique suggestions in this thread. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. And you'll want to get the three books described in this thread as soon as you can.
mrhollywood
Well-Known Member
the advance is set around 10 degrees,the spark plugs are the NGK ones you recommend slantsixdan. I dont know what the idle speed is set at right now... i need a tach.
slantsixdan
=..=
10° is a fair amount of advance given that the factory spec is between 0° and 2.5°. It's not usually enough to cause a dieseling problem, but if there are other things contributing towards the problem, the extra advance will certainly not help. How's the idle quality? Smooth and even? Rough and shaky? Watch the engine as it idles and listen at the tailpipe for the spluttering sound of misfire that would point towards vacuum leaks or improper idle settings aggravating the problem.
The direct cause of dieseling is overly-hot combustion chambers. A lot of different things can heat them up. Anything that makes a cylinder run lean, for example, will heat it up. Carbon buildup in the combustion chamber will do the same, and a bit of carbon heated to incandescence will cause the dieseling effect.
Until you find and fix the problem(s), shut the car off before you shift into Park. The transmission load on the engine will drag it down to an immediate stop.
The direct cause of dieseling is overly-hot combustion chambers. A lot of different things can heat them up. Anything that makes a cylinder run lean, for example, will heat it up. Carbon buildup in the combustion chamber will do the same, and a bit of carbon heated to incandescence will cause the dieseling effect.
Until you find and fix the problem(s), shut the car off before you shift into Park. The transmission load on the engine will drag it down to an immediate stop.
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