choke pull off
March 29th, 2008, 07:10 AM
#1
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choke pull off
I have noticed that my car idols high when you fire it up. a combination between reeving it up several times and i think just warming up, it settles down.
is this normal? or could the choke pull off be bad? is this even what the choke pull off is for? what do you think. thanks chris p.s. its a 65 olds dynamic 88 with 425 2bbl.
is this normal? or could the choke pull off be bad? is this even what the choke pull off is for? what do you think. thanks chris p.s. its a 65 olds dynamic 88 with 425 2bbl.
March 29th, 2008, 08:13 AM
#2
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Well, since it settles down with some action the pull-off is probably working. I think what might be bothering you is that it idles too high. Or did I mis-understand you? All it might require is a minor adjustment of the choke idle speed. If on the other hand, where you asking about the pull-off acting too quickly?
March 29th, 2008, 09:16 AM
#3
Oldsdruid
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Choke pull-off 101:
Its sole function in life is to open the choke plate 1/8" or so after the engine starts and builds vacuum, so the engine gets enough air to run. If it were bad, the car would run poorly if at all until the choke thermostat warmed up enough to open the choke plate. To see if it works, observe it while a helper starts the engine. If it's working, it should pull its linkage back into its vacuum diaphram chamber immediately after the engine starts.
The choke stat may be worn out or misadjusted, or even burned out. It's a simple fix, if you can find one. Genuine Rochester parts are your best bet, as a lot of aftermarket pieces are now one-size-fits-all. If it's not heating up and expanding its spring, choke and fast idle time may last longer than design.
Fast idle speed is controlled by the fast idle cam and speed screw, located behind the choke stat. All that stuff may be gummed up and sticking. Spray some choke cleaner or WD40 on it and see if it frees up. Get a 65 shop manual, and it will tell you how to adjust the fast idle speed.
65's also have a choke air filter which may be plugged. If the choke assembly can't pull in fresh air thru the heat tube, warmup will be very slow, and you run a real risk of burning out the choke heat tube in the intake.
Its sole function in life is to open the choke plate 1/8" or so after the engine starts and builds vacuum, so the engine gets enough air to run. If it were bad, the car would run poorly if at all until the choke thermostat warmed up enough to open the choke plate. To see if it works, observe it while a helper starts the engine. If it's working, it should pull its linkage back into its vacuum diaphram chamber immediately after the engine starts.
The choke stat may be worn out or misadjusted, or even burned out. It's a simple fix, if you can find one. Genuine Rochester parts are your best bet, as a lot of aftermarket pieces are now one-size-fits-all. If it's not heating up and expanding its spring, choke and fast idle time may last longer than design.
Fast idle speed is controlled by the fast idle cam and speed screw, located behind the choke stat. All that stuff may be gummed up and sticking. Spray some choke cleaner or WD40 on it and see if it frees up. Get a 65 shop manual, and it will tell you how to adjust the fast idle speed.
65's also have a choke air filter which may be plugged. If the choke assembly can't pull in fresh air thru the heat tube, warmup will be very slow, and you run a real risk of burning out the choke heat tube in the intake.
March 29th, 2008, 10:40 AM
#4
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oldsguy, i was trying to figure out why the car is idoling so high when first started and after a few reeves it settles down. i did not know if it had anything to do with the coke valve or what. i have adjusted the idol screw in past. maybe it needs it again. just did not know what would be causing it to be high then settle down after a couple reevs. chris.
Last edited by dynamic88; March 29th, 2008 at 10:44 AM.
April 9th, 2008, 09:20 AM
#6
Oldsdruid
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Just re-read this post and I'm thinking Dynamic88 may not be familiar with a carbureted car or may have been driving fuel injected cars so long he's forgotten. They need to fast idle when the engine is first started cold, in order to keep it from stalling.
The fast idle cam etc is linked to the choke thermostat. When the automatic choke is set by pressing the gas pedal to the floor before starting the engine, it moves the fast idle cam to a step that keeps the engine running about 1000 rpm or so until it stabilizes and can stay running. As the choke stat warms up, its spring tension also acts against the fast idle cam so that when you tap the gas pedal, idle speed should decrease to normal idle speed. Once the choke stat is fully hot and spring extended, the choke plate should be fully open and idle speed should be normal slow idle. If it takes longer than a minute, I'd suspect a bad or misadjusted choke stat.
A very remote possibility is that the carburetor heat crossover passage in the intake is plugged with carbon or soot and is not allowing hot exhaust gas to heat the fresh air going thru the choke hot air tube. The hot air tube could also be burned out though you'd notice that as an exhaust leak. A burned out tube can cause excessive fast idle time since the hot exhaust gas is getting into the carb and probably plugging the vacuum passage that draws heated air across the choke stat.
I know some people who insist a car should be allowed to warm up till the choke is fully open before driving off. I don't subscribe to that idea. Let engine speed stabilize, get it off fast idle and you should be able to drive away with no problems as long as you maintain a moderate (30-40 miles per hour) speed until engine is warm.
The fast idle cam etc is linked to the choke thermostat. When the automatic choke is set by pressing the gas pedal to the floor before starting the engine, it moves the fast idle cam to a step that keeps the engine running about 1000 rpm or so until it stabilizes and can stay running. As the choke stat warms up, its spring tension also acts against the fast idle cam so that when you tap the gas pedal, idle speed should decrease to normal idle speed. Once the choke stat is fully hot and spring extended, the choke plate should be fully open and idle speed should be normal slow idle. If it takes longer than a minute, I'd suspect a bad or misadjusted choke stat.
A very remote possibility is that the carburetor heat crossover passage in the intake is plugged with carbon or soot and is not allowing hot exhaust gas to heat the fresh air going thru the choke hot air tube. The hot air tube could also be burned out though you'd notice that as an exhaust leak. A burned out tube can cause excessive fast idle time since the hot exhaust gas is getting into the carb and probably plugging the vacuum passage that draws heated air across the choke stat.
I know some people who insist a car should be allowed to warm up till the choke is fully open before driving off. I don't subscribe to that idea. Let engine speed stabilize, get it off fast idle and you should be able to drive away with no problems as long as you maintain a moderate (30-40 miles per hour) speed until engine is warm.
April 9th, 2008, 11:38 AM
#7
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rocktraider, thanks for the good info. i am not familiar with the choke thermostats. it appears i have a electric one. i will have to watch next time i start up car and see if it settles down after a minute. thanks chris
April 10th, 2008, 07:00 PM
#9
Oldsdruid
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OK- if you have an electric choke stat, make sure it's getting power ONLY when the ignition switch is in RUN. Also make sure it's grounded. Aftermarkets have a ground wire; OEM grounds thru the choke housing so electric units have no insulator gasket between the housing and the stat. This is also a good time to make sure the small engine-to-frame or firewall ground straps are in place.
See if there's an index mark on the choke stat. If there is, align it with the correct notch on the choke housing. 1965 shop book calls for "index" setting on everything but stick cars, meaning you align the mark on the stat with the middle notch on the housing.
If it has no indexing mark, or if adjusting it by the index mark is obviously too lean or too rich:
Engine warm enough for choke to be fully open and normal idle speed, engine stopped, aircleaner off.
Loosen the 3 choke stat screws, hold the fast idle cam up out of the way, and slowly rotate the choke stat in RICH direction until the choke flap closes and is just lightly touching the air horn. Then move the stat one more notch rich and tighten the choke stat retaining screws. That will give you a baseline adjustment to work with.
You can then tune the choke stat to give the desired fast idle and choke time.
See if there's an index mark on the choke stat. If there is, align it with the correct notch on the choke housing. 1965 shop book calls for "index" setting on everything but stick cars, meaning you align the mark on the stat with the middle notch on the housing.
If it has no indexing mark, or if adjusting it by the index mark is obviously too lean or too rich:
Engine warm enough for choke to be fully open and normal idle speed, engine stopped, aircleaner off.
Loosen the 3 choke stat screws, hold the fast idle cam up out of the way, and slowly rotate the choke stat in RICH direction until the choke flap closes and is just lightly touching the air horn. Then move the stat one more notch rich and tighten the choke stat retaining screws. That will give you a baseline adjustment to work with.
You can then tune the choke stat to give the desired fast idle and choke time.
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