67 Cutlass loads up
April 11th, 2015, 12:29 PM
#1
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67 Cutlass loads up
I have a 67 330 2bbl. Car runs great except if I leave it running for 10-15 minutes @ idle. Then it seems to load up & pops & won't run well under load but idles fine. Takes a couple of mile to clear.
Haven't pulled the air cleaner off to check how the choke works when cold but does not start normal when cold. Only had car for a short time & the weather has been bad.
Don-M
Haven't pulled the air cleaner off to check how the choke works when cold but does not start normal when cold. Only had car for a short time & the weather has been bad.
Don-M
April 11th, 2015, 02:00 PM
#3
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Join Date: Dec 2011
Posts: 7,286
Make sure the ignition is up to snuff- points are newish and set right, timing set right, plug wires are not too leaky... rot like that.
If it does not start right when cold then you should look into the choke operation, starting with, when cold, does it snap shut when you blip the throttle before activating the starter?
How much do you know already about how the choke should work? It should be the big black disc type spring element like later 4-bbls used, and easy to check for correct operation.
Don't put your head above the carb on a running or cranking engine [fire]
If it does not start right when cold then you should look into the choke operation, starting with, when cold, does it snap shut when you blip the throttle before activating the starter?
How much do you know already about how the choke should work? It should be the big black disc type spring element like later 4-bbls used, and easy to check for correct operation.
Don't put your head above the carb on a running or cranking engine [fire]
April 11th, 2015, 02:01 PM
#4
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Thanks, I will. I know that the chock plate should close & the high idle cam should work as well as a liknage called the choke puller should open the plate open slightly on startup after pedal is floored. Correct?
Last edited by Kid Thunder; April 11th, 2015 at 02:09 PM.
April 12th, 2015, 08:14 AM
#5
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Posts: 7,286
Almost
When cold, the choke spring should close the choke, thereby dropping the fast idle cam into play as soon as the throttle is opened a bit. This can all be observed w/o the danger of a running engine.
Choke should now be totally closed.
If you open the throttle all the way, like pedal to the metal, which is best done at the carb with your hand, engine still not running... the unloader feature should prop the choke open about 1/4" to allow air into a flooded engine, should that ever occur. Rarely used but essential feature.
Release throttle to the closed-choke high idle condition
One can now use the vacuum pump to pull on the choke pulloff diaphragm and verify that it opens the choke the specified amout [see CSM or rebuild kit figures].... or simply start the engine and see that the engine vacuum performs this function.
Within a minute or three of running, the choke spring should start to relax, allowing the fast idle cam to work its way down to shorter steps whenever the FI screw is pulled up off it by e.g. blipping the throttle. At some point near fully open choke the FI cam will no longer engage its mating aduster screw and the idle setting will be taken up by the driver side [primary] idle speed setting screw.
Remember that pretty much every feature of a carb runs on vacuum.
Engine timing affects the vacuum developed at idle, which is why I urged you to ensure that the points, dwell, and timing are all in order. That usually goes hand in hand with one thing I left out- the vacuum gage readings. Proper timing produces steady high vacuum. Poor [retarded] timing provides low and fluctuating readings.
The carb depends on vacuum to operate properly.
In my case, the vacuum was evidently dropping so low that the throttle plates had to be cracked open so far that the idle ports were no longer in charge of accurately metering the fuel. I suspect that at the low readings I observed [8-9"], the power piston was no longer held down, thus allowing more fuel thru the main jets [which should not even be used at idle...] The viscious cycle continues, with richer mixture causing poor idle causing low vacuum causing richer mixture.... until it dies.
The solution involved attaching the distributor vacuum to manifold source. Voila... late timing while cranking makes starting easy... increased timing as soon as the engine starts
More vacuum = proper carb functions
Carb butterflies can be set more closed so that the idle circuit is used.
Overheating stops
loading to rich then dying cycle stops
Life is good in America, and the streets are paved with gold.
When cold, the choke spring should close the choke, thereby dropping the fast idle cam into play as soon as the throttle is opened a bit. This can all be observed w/o the danger of a running engine.
Choke should now be totally closed.
If you open the throttle all the way, like pedal to the metal, which is best done at the carb with your hand, engine still not running... the unloader feature should prop the choke open about 1/4" to allow air into a flooded engine, should that ever occur. Rarely used but essential feature.
Release throttle to the closed-choke high idle condition
One can now use the vacuum pump to pull on the choke pulloff diaphragm and verify that it opens the choke the specified amout [see CSM or rebuild kit figures].... or simply start the engine and see that the engine vacuum performs this function.
Within a minute or three of running, the choke spring should start to relax, allowing the fast idle cam to work its way down to shorter steps whenever the FI screw is pulled up off it by e.g. blipping the throttle. At some point near fully open choke the FI cam will no longer engage its mating aduster screw and the idle setting will be taken up by the driver side [primary] idle speed setting screw.
Remember that pretty much every feature of a carb runs on vacuum.
Engine timing affects the vacuum developed at idle, which is why I urged you to ensure that the points, dwell, and timing are all in order. That usually goes hand in hand with one thing I left out- the vacuum gage readings. Proper timing produces steady high vacuum. Poor [retarded] timing provides low and fluctuating readings.
The carb depends on vacuum to operate properly.
In my case, the vacuum was evidently dropping so low that the throttle plates had to be cracked open so far that the idle ports were no longer in charge of accurately metering the fuel. I suspect that at the low readings I observed [8-9"], the power piston was no longer held down, thus allowing more fuel thru the main jets [which should not even be used at idle...] The viscious cycle continues, with richer mixture causing poor idle causing low vacuum causing richer mixture.... until it dies.
The solution involved attaching the distributor vacuum to manifold source. Voila... late timing while cranking makes starting easy... increased timing as soon as the engine starts
More vacuum = proper carb functions
Carb butterflies can be set more closed so that the idle circuit is used.
Overheating stops
loading to rich then dying cycle stops
Life is good in America, and the streets are paved with gold.
Last edited by Octania; April 12th, 2015 at 08:28 AM.
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