Sudden Q-Jet cold start problem, 1972
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From: Camp Verde AZ
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Sudden Q-Jet cold start problem, 1972
Started and ran fine until yesterday; blowing black smoke and wouldn't run the next morning at start.
I simply wired the choke open to get it to run, though you need to warm up the motor prior to driving it. Car runs flawlessly still when warm.
Besides a failure in the vacuum pot that pulls the choke open after the car is started, would anything else cause a sudden cold start problem due to running way, way too rich?
BTW, the pot pulls itself all the way in, at least with a warm motor, so the pot seems OK.
Thanks,
Doug
I simply wired the choke open to get it to run, though you need to warm up the motor prior to driving it. Car runs flawlessly still when warm.
Besides a failure in the vacuum pot that pulls the choke open after the car is started, would anything else cause a sudden cold start problem due to running way, way too rich?
BTW, the pot pulls itself all the way in, at least with a warm motor, so the pot seems OK.
Thanks,
Doug
Last edited by AZDoug; Sep 26, 2011 at 04:47 PM.
Thread Starter
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Joined: Oct 2005
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From: Camp Verde AZ
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2017 C1 of Year Finalist
Safety Car
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From: NorCal
Choke pull-off
The choke pull-off (pot) can be checked easily and has to be working perfectly to keep the "flooding" or rich condition cold from happening.
Pull the air cleaner assembly before you start it cold. set the choke by giving it enough throttle for it to close. Once it's closed, make sure the blade moves freely by poking it with your finger or a screwdriver. Fire it up, or better yet, have a helper do it and watch the choke butterfly and pull-off. the pull-off should snap the choke open about 3/16 or so and the throttle should be on high idle as usual. If the chke stays shut or is lazy, put a new pull-off on it!
You can check the pull-off with a vacuum pump, or just hook a long hose to it suck on that to see if it holds. It should not leak at all. They can look like they're working, but not have any pulling power at all.
If all that is working, then move on to the well plugs. The fact that it happened all at once tells me it's the pull-off, or the choke itself is hanging up.
Hans
Pull the air cleaner assembly before you start it cold. set the choke by giving it enough throttle for it to close. Once it's closed, make sure the blade moves freely by poking it with your finger or a screwdriver. Fire it up, or better yet, have a helper do it and watch the choke butterfly and pull-off. the pull-off should snap the choke open about 3/16 or so and the throttle should be on high idle as usual. If the chke stays shut or is lazy, put a new pull-off on it!
You can check the pull-off with a vacuum pump, or just hook a long hose to it suck on that to see if it holds. It should not leak at all. They can look like they're working, but not have any pulling power at all.
If all that is working, then move on to the well plugs. The fact that it happened all at once tells me it's the pull-off, or the choke itself is hanging up.
Hans
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From: Camp Verde AZ
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The vac pot is my main suspect at this point. I agree eliminate it before digging deeper.
Just so i know that everything is correct before I do a cold start check tomorrow, does the vac pot connect to the vacuum port right next to the fuel inlet nut?
Thanks,
Doug
Just so i know that everything is correct before I do a cold start check tomorrow, does the vac pot connect to the vacuum port right next to the fuel inlet nut?
Thanks,
Doug
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From: Camp Verde AZ
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2017 C1 of Year Finalist
Something else:
Checking choke adj in the service manual.
With the cam follower on the second step of the fast idle cam, there is a lot of play in the choke mechanism (down inside the side of the carb where you can't see it), you can move the choke to full closed from about 3/16" open on the bottom side, without any external movement in the external linkage, the rod and lower inside lever move, but don't transfer that movement to the external levers.
Is that normal?
With the thermo spring rod pulled down tight, and the follower on the second step, the choke is completely, totally closed. This also removed the slop I mentioned above, you cannot open the choke plate unless the thermo spring rod moves up.
The service manual suggests that i shouldn't be able to push the choke all the way closed with the cam follower on the second step.
Again, the car started fine Saturday morning and was a pain to start Sunday morning.
Thanks,
Doug
Checking choke adj in the service manual.
With the cam follower on the second step of the fast idle cam, there is a lot of play in the choke mechanism (down inside the side of the carb where you can't see it), you can move the choke to full closed from about 3/16" open on the bottom side, without any external movement in the external linkage, the rod and lower inside lever move, but don't transfer that movement to the external levers.
Is that normal?
With the thermo spring rod pulled down tight, and the follower on the second step, the choke is completely, totally closed. This also removed the slop I mentioned above, you cannot open the choke plate unless the thermo spring rod moves up.
The service manual suggests that i shouldn't be able to push the choke all the way closed with the cam follower on the second step.
Again, the car started fine Saturday morning and was a pain to start Sunday morning.
Thanks,
Doug
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Thread Starter
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From: Camp Verde AZ
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Something changed.
Doug
Melting Slicks
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From: Austin Tx
Lars is by far the best reference when it comes to carbs, here is a link to one of his papers - http://www.lbfun.com/warehouse/tech_...ng%20Paper.pdf
