Hey guys, ive got a '66 200 A/T, just had the carb rebuilt. Every so often after i drive it and turn it off the engine will sputter and jump a bit...sometimes its short, sometimes long...it varies but nonetheless its driving me crazy. Anyways, id really appreciate any help. Thanks in advance.
Car sputters when key turned off
- Thread starter jtan540
- Start date
If lowering the Idle speed doesent fix the problem , bump up the octane of the fuel your using , in my opinion all older cars due to their limited use should use 91 min, This is NOT an ignition problem , so playing with the timing is not a fix , Dieseling is a run on condition with out the need for spark , I have also seen cases where a Electic fan feeds back through the ign circut untill it spins down, hope this helps
If I understand you correctly, it's trying to keep running after shutting off the ignition? It could be a throttle plate not closing completely, or fuel sloshing into the engine from a float set too high. This would be compounded by a litttle fuel boiling over from a too-hot engine/thermostat. What's your temperature read? Odds are something is not completely right with your carb. I always say to suspect the last thing worked on, when a new problem arises following maintenance.
Well this problem has been occuring ever since I got the car, before the carb was rebuilt. But you are right, it does seem like the car wants to continue running even though the ignition is off, and the thermostat reads smack dab in the middle...so i will check the throttle plate and see if it is closing properly
There is a very small screw under the carb that controls how tightly the blade closes. This is normally not adjusted, but.... Have you checked your float settings?
To keep it from doing that you can leave it in gear when you turn off the key. Its not a fix but at least it will keep you from looking like Uncle Buck when you shut it off. Just remember to put it in park before you take your foot off the brake and get out.
What do the spark plugs look like? Im thinking you got a big carbon build up.
What do the spark plugs look like? Im thinking you got a big carbon build up.
66 Fastback
Famous Member
Dieseling is a combination of the throttle plates not being closed sufficiently, and high cylinder temps, hot spots in the cylinder or spark plugs that are retaining too much heat. The fuel is igniting on its own due to a hot spot or high cylinder temps and the fact that it is able to draw fuel in through the carb.
The high heat could be due to carbon buildup, vacuum leaks or lean mixtures and insufficient cooling. But often, it is improper (retarded) timing resulting in higher cyl head temps at idle. If your vac advance is not operating correctly and not advancing the timing at idle, then the temptation is to raise the idle speed by screwing in the throttle plate idle stop which smooths out the idle. When the ignition is shut off, the plates are open enough, allowing air to carry more fuel into the engine, where it is spontaneously igniting due to the high cylinder temps.
Check to make sure your throttle plates are closed sufficiently. Check your timing, retarded timing makes the engine run hotter. Make sure the vacuum motors on the distributor are working. Advancing the timing will smooth out and increase the idle speed allowing you to back off the idle adjustment and close the throttle plates more.
Where is your distributor vacuum line connected too? If necessary, you might hook the advance side of the vacuum line up to a manifold vacuum source in order to get more advance at idle. Doing so will advance the timing and smooth out the idle allowing you to close the throttle plates more.
Doug
The high heat could be due to carbon buildup, vacuum leaks or lean mixtures and insufficient cooling. But often, it is improper (retarded) timing resulting in higher cyl head temps at idle. If your vac advance is not operating correctly and not advancing the timing at idle, then the temptation is to raise the idle speed by screwing in the throttle plate idle stop which smooths out the idle. When the ignition is shut off, the plates are open enough, allowing air to carry more fuel into the engine, where it is spontaneously igniting due to the high cylinder temps.
Check to make sure your throttle plates are closed sufficiently. Check your timing, retarded timing makes the engine run hotter. Make sure the vacuum motors on the distributor are working. Advancing the timing will smooth out and increase the idle speed allowing you to back off the idle adjustment and close the throttle plates more.
Where is your distributor vacuum line connected too? If necessary, you might hook the advance side of the vacuum line up to a manifold vacuum source in order to get more advance at idle. Doing so will advance the timing and smooth out the idle allowing you to close the throttle plates more.
Doug
HUMINA
Active member
As I understand dieseling (car continues to spit and sputter after the ignition is cut off) is primarily caused by hot spots in the combustion chamber. Once the ignition is shut off, it shouldn't matter if more fuel is making it to your cylinder. Only diesels should be able to run without a spark.
It is typically associated with engines that have been running for quite some time and have some carbon build up in the cylinder. The carbon holds just enough heat to allow combustion in a hot engine.
Modern high mileage engines shouldn't ever have this problem because the electric fuel pump is killed when the ignition switch is off.
My father had a chevy van with a three on the tree that developed this problem after a 175000 miles or so and he would often leave it in gear with is foot on the clutch and brake. When he shut the ignition off he would release the clutch with his foot on the brake. Any small load on the engine would kill it immediately.
It is typically associated with engines that have been running for quite some time and have some carbon build up in the cylinder. The carbon holds just enough heat to allow combustion in a hot engine.
Modern high mileage engines shouldn't ever have this problem because the electric fuel pump is killed when the ignition switch is off.
My father had a chevy van with a three on the tree that developed this problem after a 175000 miles or so and he would often leave it in gear with is foot on the clutch and brake. When he shut the ignition off he would release the clutch with his foot on the brake. Any small load on the engine would kill it immediately.
66 Fastback
Famous Member
Some of the emission era carbureted cars where equipped with anti-deiseling solenoids to close the throttle or shut off the fuel supply. They had leand out the mixtures and retarded the timing to combat the hydrocarbon emissions to the point that the cars ran hot at idle and had difficulty idling unless the throttle plates were openned more. So the band aid was to install another solenoid to close the throttle plates to prevent the engine run-on. They addressed the fire triangle Air, Heat & Fuel. Given that they were stuck with the higher heat for emission purposes, that took out the two other sides of the triangle by removing fuel and air from the equation. The engine did not necessarily have to have carbon deposits causing the ignition.
Doug
When I do turn off the ignition on drive, the car does not sputter. I did change the spark plugs recently and boy oh boy were they gone. Carbon fouled, yes...also a bit black...since the previous owner had no recognition of where the fill line was so he just kept on toppping off the oil since there is a leak in the gasket. So with that being said I popped in new gapped autolites. But anyways, I checked the carb and the throttle plate is properly closing. What would be the best way of going about cleaning the carbon buildup? Thanks for all your help
I cleaned up carbon deposits in my engine by pouring a capful or two of automatic transmission fluid down the carb (slowly) with the engine running and my hand on the accel. linkage to keep it running while pouring. This produces quite a bit of black and then blue (possibly white) smoke. Keep the throttle open enough to not stall while pouring.
horsin' around":3hymy4f7 said:
I too have used this old trick before (using as much as 1/4 qt. or about a cup full). Once on an engine that had been run with two spark plug wires crossed for a month. It has been very effective for me in producing large clouds of black smoke on heavily carboned engines. IIRC, dextron works better than type F in this situation, and it's a bit easier if you have someone who can throttle it up while you pour..."slowly" is the key.
66 Fastback
Famous Member
I had not heard of removing carbon with transmission fluid. Wouln't that add carbon build up as the oil meets the hot combustion chamber? I have always heard of using water. The water supposedly boils and also cracks off some of the carbon as it cools it and immediately boils off.
Doug
Doug
66 Fastback":x4wqzwz9 said:
Nah. The transmission fluid acts as a mild solvent. If your engine is sludged up, a pint or so in the oil will break loose a lot of junk. Of course, if that junk is plugging leaks, you will start to leak oil.
Though, I would rather use water in the intake.
I like the water, much less messy and dangerous if you over do it and it pops back through the carb. A regular spray bottle set to mist works great.
Pull a couple of the new plugs and see if they are showing signs of looking bag again.
Pull a couple of the new plugs and see if they are showing signs of looking bag again.
For me this was sort of a home remedy passed down by an old mechanic. I don't know if it's the caustic quality of the ATF (that also seems to make it such a good cleaner), or detergents, or what...but it did seem to provide the desired result. I actually had the opportunity to examine cylinders and pistons of an engine that had been previously de-carboned with ATF, and you could see the effects. It was not a perfect cleaning, but there were areas of the cumbustion chambers where it appeared large patches of carbon had been burned off.
Edit: This was used straight into the carb in small amounts while engine is running @ or above normal operating temp...just like you would with the 'steam cleaning'/h2o approach.
A similar experience in using ATF in a combustion chamber, was when I had trouble getting a wankel to fire over that had sat too long, and then been flooded. I had tried using oil in the 'cylinder', as it were, to help reset/reseal the rotor tips/seals with no success. Took it to a stealership and they used ATF in the combustion chamber to get it to fire up. I seem to recall the mechanic saying the ATF did not prohibit combustion or burned more readily than the oil would. Yet another in the 'snake oil claims' of ATF was a friend who unseized an engine by putting ATF in the cylinders to free the rings. Don't mean to make out like ATF as a miracle panacea, the next best thing since sliced bread, or even as good as a Ronco Pocket Fisherman
...but personally I have seen good results from these type of uses. I know others prefer something more like a seafoam type of product for de-carboning the engine.
Edit: This was used straight into the carb in small amounts while engine is running @ or above normal operating temp...just like you would with the 'steam cleaning'/h2o approach.
A similar experience in using ATF in a combustion chamber, was when I had trouble getting a wankel to fire over that had sat too long, and then been flooded. I had tried using oil in the 'cylinder', as it were, to help reset/reseal the rotor tips/seals with no success. Took it to a stealership and they used ATF in the combustion chamber to get it to fire up. I seem to recall the mechanic saying the ATF did not prohibit combustion or burned more readily than the oil would. Yet another in the 'snake oil claims' of ATF was a friend who unseized an engine by putting ATF in the cylinders to free the rings. Don't mean to make out like ATF as a miracle panacea, the next best thing since sliced bread, or even as good as a Ronco Pocket Fisherman
...but personally I have seen good results from these type of uses. I know others prefer something more like a seafoam type of product for de-carboning the engine.
I have heard of it being put in gas tanks as well, over on BITOG.
I would not be surprised if there are ATF-like substances in upper cylinder lubricant products like Lucas and Redline.
I understand it makes a good rust protectant, that was recommended by a machinist who had just cleaned a block for me.
I would not be surprised if there are ATF-like substances in upper cylinder lubricant products like Lucas and Redline.
I understand it makes a good rust protectant, that was recommended by a machinist who had just cleaned a block for me.
66 Fastback
Famous Member
I can attest to the anti-corrosion properties. My cars with leaky automatic transmissions covered in ATF have no rust on the pan.
Doug
