Fast idle adjustment?
Thread Starter
Burning Brakes
Joined: Dec 2006
Posts: 931
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From: THE Eastern Shore Maryland
Fast idle adjustment?
Our 76 still has the original Rochester carb. It idles about 650 to 700 rpms when warm, now that I adjusted it down a bit, so thats good.
The problem is the fast idle. It fast idles about 1500 rpm when cold, and I'm not sure how to adjust it down. I thought I found the correct adjustment screw but it doesn't seem to bring it down.
Any ideas?
The problem is the fast idle. It fast idles about 1500 rpm when cold, and I'm not sure how to adjust it down. I thought I found the correct adjustment screw but it doesn't seem to bring it down.
Any ideas?
Le Mans Master
Joined: Oct 2006
Posts: 7,123
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From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Make sure the choke pull off is opening the choke plate after it starts and holding it open, then the screw on the right side should be it. Sorry I don't have any pics, maybe someone has a good pic of the right side of a Q-Jet that they can post.
Thread Starter
Burning Brakes
Joined: Dec 2006
Posts: 931
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From: THE Eastern Shore Maryland
The butterfly partially closes and it fast idles as its supposed to do, (too high however), and it kicks down when warm, like its supposed to do. It should fast idle around 1100 rpms or so, I just need to get it down to that.
Race Director
Joined: Sep 2002
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From: San Diego - Deep Within The State of CONFUSION!
The fast idle adjustment is on the pass. side of the carb bottom left.
Drifting
Joined: Mar 2006
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From: Oak Ridge NC
Thread Starter
Burning Brakes
Joined: Dec 2006
Posts: 931
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From: THE Eastern Shore Maryland
Well it turns out the fast idle is the screw I thought it was fellas. I just didn't turn it enough to make a difference.
I had to turn it counter clockwise 2 full screw turns to make it fast idle down to about 1100 rpms. If I did 2 1/2 it didn't want to start...so it seems right now about 1100 rpms is about as low fast idle that I can go...it was actually about 1600 rpms before.
I had to turn it counter clockwise 2 full screw turns to make it fast idle down to about 1100 rpms. If I did 2 1/2 it didn't want to start...so it seems right now about 1100 rpms is about as low fast idle that I can go...it was actually about 1600 rpms before.
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Thread Starter
Burning Brakes
Joined: Dec 2006
Posts: 931
Likes: 0
From: THE Eastern Shore Maryland
Update on my fast idle saga.
I turned it two full turns counter clockwise yesterday and it seemed ok, a bit high still.
I go out this morning and it turned over and started for a sec, then shutdown, did it again, same thing. Started it again and it fast idled about 1500 rpms.
Maybe thats the reason the previous owner had it set so high, because if you don't it won't idle correctly, not that 1500rpms is correct. If I get it down to a lower number it won't start initially for the first few times, at least.
The previous owner used to bring it to a shop for everthing and he said thats what it is supposed to fast idle at.
The fast idle saga continues, lol.
I turned it two full turns counter clockwise yesterday and it seemed ok, a bit high still.
I go out this morning and it turned over and started for a sec, then shutdown, did it again, same thing. Started it again and it fast idled about 1500 rpms.
Maybe thats the reason the previous owner had it set so high, because if you don't it won't idle correctly, not that 1500rpms is correct. If I get it down to a lower number it won't start initially for the first few times, at least.
The previous owner used to bring it to a shop for everthing and he said thats what it is supposed to fast idle at.
The fast idle saga continues, lol.
Last edited by jetdoc; Apr 30, 2007 at 08:29 AM.
Thread Starter
Burning Brakes
Joined: Dec 2006
Posts: 931
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From: THE Eastern Shore Maryland
Lyle, the guy had detailed the entire engine bay with black paint, so if there were one it has been painted over, so I don't know.
I didn't consider that 1500 rpms could be normal for the 76, I do know my 73 doesn't fast idle that high...I will go and see if my 73 still has the plate near master cyl?
I will do some more digging.
I didn't consider that 1500 rpms could be normal for the 76, I do know my 73 doesn't fast idle that high...I will go and see if my 73 still has the plate near master cyl?
I will do some more digging.
Tech Contributor
Joined: Aug 1999
Posts: 14,366
Likes: 6,348
From: At my Bar drinking and wrenching in Lafayette Colorado
If it dies when you start it cold, you don't have a fast idle issue - you have a choke pulloff adjustment issue. Make sure your pulloff is working (many are ruptured) and make sure it's set to open the choke 1/4" upon cold start. Once this is set, you can adjust the fast idle.
If you need specific instructions, you can e-mail me for my Q-Jet Choke Setup paper:
V8FastCars@msn.com
If you need specific instructions, you can e-mail me for my Q-Jet Choke Setup paper:
V8FastCars@msn.com
Thread Starter
Burning Brakes
Joined: Dec 2006
Posts: 931
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From: THE Eastern Shore Maryland
Lars, an email to you my friend.
Lets back up....the car always starts up and idles, all be it at a high RPM it seems. It has never died when I started it until I backed down the fast idle adjustment screw, (trying to get it from 1500rpms to 1100rpms).
If I put the fast idle adjustment to where it was originally then it starts fine, it just fast idles @ 1500rpms...then kicks down to about 700rpms when warm.
Just wanted to make that clear Lars, it never had a dying out issue at all, that is until I backed the fast idle screw down.
Lets back up....the car always starts up and idles, all be it at a high RPM it seems. It has never died when I started it until I backed down the fast idle adjustment screw, (trying to get it from 1500rpms to 1100rpms).
If I put the fast idle adjustment to where it was originally then it starts fine, it just fast idles @ 1500rpms...then kicks down to about 700rpms when warm.
Just wanted to make that clear Lars, it never had a dying out issue at all, that is until I backed the fast idle screw down.
Last edited by jetdoc; May 1, 2007 at 08:58 AM.
Thread Starter
Burning Brakes
Joined: Dec 2006
Posts: 931
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From: THE Eastern Shore Maryland
Last edited by jetdoc; May 1, 2007 at 10:26 AM.
Thread Starter
Burning Brakes
Joined: Dec 2006
Posts: 931
Likes: 0
From: THE Eastern Shore Maryland
The screw Im adjusting is on the passenger side, up on top area. Its right behind and attached via linkage to a diaphram and above the rich/lead choke adjustment.
Still trying to adjust before I have to go to work. Seems a bit better. I thought If I turned screw all the way clockwise till spring is full extended, then back out 2 1/2 turns that is a good starting point.
It seems better as I said but if I am sitting in car and slam gas pedal hard it hesitates. Start off moderately and its ok....to be honest I've never just slammed the pedal down before, so Im not sure if it did that before or not.
****Just got back from a nice ride, had it up to 80 and it seems ok. If I start off as I normally do, and always have, there is no hesitation and it doesn't smell rich and no back fire going on either.
Seems going all the way down and back out 2 1/2 turns did the trick. It may not be perfect but its a lot better than before. I will see how it fast idles in the morning. It starts hot ok.
I know I'm doing a lot of talking to myself, but thats normal for me,
.
Still trying to adjust before I have to go to work. Seems a bit better. I thought If I turned screw all the way clockwise till spring is full extended, then back out 2 1/2 turns that is a good starting point.
It seems better as I said but if I am sitting in car and slam gas pedal hard it hesitates. Start off moderately and its ok....to be honest I've never just slammed the pedal down before, so Im not sure if it did that before or not.
****Just got back from a nice ride, had it up to 80 and it seems ok. If I start off as I normally do, and always have, there is no hesitation and it doesn't smell rich and no back fire going on either.
Seems going all the way down and back out 2 1/2 turns did the trick. It may not be perfect but its a lot better than before. I will see how it fast idles in the morning. It starts hot ok.
I know I'm doing a lot of talking to myself, but thats normal for me,
.
Last edited by jetdoc; May 1, 2007 at 11:33 AM.
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
Thread Starter
Burning Brakes
Joined: Dec 2006
Posts: 931
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From: THE Eastern Shore Maryland
Lars: "That's not the correct adjustment. You need to set it to open the choke blade 1/4" as measured from the forward lower edge of the choke plate to the airhorn wall with vacuum applied to the pulloff. Your 2-1/2 turn setting wil not work correctly. You need to set the choke up right."
me: I know normally when I go out to the car in the morning the butterfly is closed two about 1/4 inch full closed. I start it up and as the engine warms the butterfly opens till its full open eventually, of course.
I will have to wait till the morning to see how closed it is now? Are you saying, Lars, that adjusting what I was wouldn't cause any engine performance problems once the engine is warm and I will have the problem in the morning? It sure seemed like it was sputtering and hesitating until I did some more adjusting on that one screw?
me: I know normally when I go out to the car in the morning the butterfly is closed two about 1/4 inch full closed. I start it up and as the engine warms the butterfly opens till its full open eventually, of course.
I will have to wait till the morning to see how closed it is now? Are you saying, Lars, that adjusting what I was wouldn't cause any engine performance problems once the engine is warm and I will have the problem in the morning? It sure seemed like it was sputtering and hesitating until I did some more adjusting on that one screw?
Last edited by jetdoc; May 1, 2007 at 04:27 PM.
Tech Contributor
Joined: Aug 1999
Posts: 14,366
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From: At my Bar drinking and wrenching in Lafayette Colorado
It will have no effect once the engine is warm. It will only affect cold performance and drivabilility when cold.
But why don't you just set up the choke correctly to the correct specs as outlined in my paper? There is no reason to be making random adjustments and guessing at the setup - there are specs for these adjustments.
But why don't you just set up the choke correctly to the correct specs as outlined in my paper? There is no reason to be making random adjustments and guessing at the setup - there are specs for these adjustments.
Last edited by lars; May 1, 2007 at 04:28 PM.
Thread Starter
Burning Brakes
Joined: Dec 2006
Posts: 931
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From: THE Eastern Shore Maryland
It will have no effect once the engine is warm. It will only affect cold performance and drivabilility when cold.
But why don't you just set up the choke correctly to the correct specs as outlined in my paper? There is no reason to be making random adjustments and guessing at the setup - there are specs for these adjustments.
But why don't you just set up the choke correctly to the correct specs as outlined in my paper? There is no reason to be making random adjustments and guessing at the setup - there are specs for these adjustments.
I am confused as to why the car was sputtering and hesitiating until I tweaked the screw a few turns here and there...I dunno?
Last edited by jetdoc; May 1, 2007 at 04:54 PM.