Idle speed changes on me
Thread Starter
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Joined: Aug 2005
Posts: 59
Likes: 5
Idle speed changes on me
I have a Q-jet that has been re-built. Also had new bushings put on the primary throttle shaft. Start the engine up warm and it idles fine at 700 rpm. Drive down the road and back and the engine wants to idle at 1000 to 1200 rpm. Push the secondary air valve open and the engine goes back to its 700 rpm idle speed. Let the air valve close and in 10 to 15 secs. the engine will start back to 1000 to 1200 rpm idle. Turn the engine off and re-start it and it will idle fine at 700 rpm,... until I drive it. Help please. Thanks
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,113
From: Crossville TN
One of three things is happening:
1. You have some binding in the throttle cable or carb side linkage; find it, lube it, and/or add a stronger return spring.
2. Your floor mat is laying on the accelerator pedal.
3. The carb is not 'centered' on the intake manifold and the throttle plates are rubbing on the bores in the manifold. Loosen the carb mounting nuts, wiggle the carb to become more centered, then tighten them back down. Now try "exercising" the throttle to see if it is any better.
4. There could be other possibilites...I just couldn't think of them.
1. You have some binding in the throttle cable or carb side linkage; find it, lube it, and/or add a stronger return spring.
2. Your floor mat is laying on the accelerator pedal.
3. The carb is not 'centered' on the intake manifold and the throttle plates are rubbing on the bores in the manifold. Loosen the carb mounting nuts, wiggle the carb to become more centered, then tighten them back down. Now try "exercising" the throttle to see if it is any better.
4. There could be other possibilites...I just couldn't think of them.
Le Mans Master
Joined: Oct 2006
Posts: 6,842
Likes: 285
From: Palmdale CA
One of three things is happening:
1. You have some binding in the throttle cable or carb side linkage; find it, lube it, and/or add a stronger return spring.
2. Your floor mat is laying on the accelerator pedal.
3. The carb is not 'centered' on the intake manifold and the throttle plates are rubbing on the bores in the manifold. Loosen the carb mounting nuts, wiggle the carb to become more centered, then tighten them back down. Now try "exercising" the throttle to see if it is any better.
4. There could be other possibilites...I just couldn't think of them.
1. You have some binding in the throttle cable or carb side linkage; find it, lube it, and/or add a stronger return spring.
2. Your floor mat is laying on the accelerator pedal.
3. The carb is not 'centered' on the intake manifold and the throttle plates are rubbing on the bores in the manifold. Loosen the carb mounting nuts, wiggle the carb to become more centered, then tighten them back down. Now try "exercising" the throttle to see if it is any better.
4. There could be other possibilites...I just couldn't think of them.
Yep, mine was number 3. The rear secondaries wouldn't quite close sometimes after opening, because the sides of the plates would stick just a little. With the extra air coming in, the idle would be higher than normal, but once it closed properly, then it was good.You could also rotate the linkage against the stop when it's idling high and/or press on the butterflies and see if you hear a change in the RPM level.
Thread Starter
Advanced
Joined: Aug 2005
Posts: 59
Likes: 5
Pressing on the primary throttle arm of the carb. (the one the throttle cable goes to) does not help, and I can see that the arm is against the set screw. So it should be back to the original setting of 700 rpm. I found that opening the secondary air valve brought the engine back to normal idle by pushing it open to look and see if the secondary throttle blades were closed. They look to be closed and pushing on the secondary throttle arm does nothing to help return the engine to normal idle. If I watch the throttle arms when the engine is shut off I see no movement. But when the engine is immediately re-started it will idle at 700 rpm. Thanks for the ideas.
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Thread Starter
Advanced
Joined: Aug 2005
Posts: 59
Likes: 5
I put an old Q-Jet that I had on the engine, and it idles great. So I guess I better see what's wrong with the re-built Q-Jet. That wasn't suppose to happen. Trying to get one fixed-up and running good and more problems.
Advanced
Joined: Mar 2007
Posts: 97
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From: Colusa Ca
yes he is doing it still you will need to send him an email to go over the details. I just emailed him last night and he said he had a few weeks lead time and I might want to hold off a week or two before i send it to him.
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
I have a Q-jet that has been re-built. Also had new bushings put on the primary throttle shaft. Start the engine up warm and it idles fine at 700 rpm. Drive down the road and back and the engine wants to idle at 1000 to 1200 rpm. Push the secondary air valve open and the engine goes back to its 700 rpm idle speed. Let the air valve close and in 10 to 15 secs. the engine will start back to 1000 to 1200 rpm idle. Turn the engine off and re-start it and it will idle fine at 700 rpm,... until I drive it. Help please. Thanks
vacuum leak.