575 Speed Demon Trottle Return Problem
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Joined: Sep 2004
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From: Minnesota
575 Speed Demon Trottle Return Problem
I have a 575 Speed Demon carb that has a problem fully returning the throttle. I put 2 return springs on the rear and 2 on the front (which makes it hard to push the pedal) and after the springs stretch it still will not return all the way on its own. If I jab the pedal it will return but that's a pain. In normal driving it will not fully return and at a stop the car idles at 1000 RPM's. If I jab the pedal it will drop to 750 RPM's (which is what I set the idle to). I do not see it binding anywhere.
Has anyone else had this problem? Any ideas on what is causing this. It has done this since it was new.
Thanks
Has anyone else had this problem? Any ideas on what is causing this. It has done this since it was new.
Thanks
Team Owner
Joined: Apr 1999
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
IMO - something is binding. It's easy to prove. Remove any linkage from the the drivers side. throttle/kickdown/TV cable the carb has a spring for pri and sec. Just see if it snaps shut.
i felt like i had two much petal effort on my 750 speed demon so i went with lighter external duals to the manifold (because the rule book requires 2) and I removed the secondary shaft spring one rotation so it's really loose.
i felt like i had two much petal effort on my 750 speed demon so i went with lighter external duals to the manifold (because the rule book requires 2) and I removed the secondary shaft spring one rotation so it's really loose.
Melting Slicks
Joined: Mar 2006
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From: Connecticut
Originally Posted by captainmorgan
Has anyone else had this problem? Any ideas on what is causing this. It has done this since it was new.
Thanks
A little lithium grease sprayed on the shaft usually cures it.
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From: Minnesota
Originally Posted by gkull
IMO - something is binding. It's easy to prove. Remove any linkage from the the drivers side. throttle/kickdown/TV cable the carb has a spring for pri and sec. Just see if it snaps shut.
i felt like i had two much petal effort on my 750 speed demon so i went with lighter external duals to the manifold (because the rule book requires 2) and I removed the secondary shaft spring one rotation so it's really loose.
i felt like i had two much petal effort on my 750 speed demon so i went with lighter external duals to the manifold (because the rule book requires 2) and I removed the secondary shaft spring one rotation so it's really loose.
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From: Minnesota
Originally Posted by Bob Onit
I have seen this with Quadrajets that have had the primary throttle shaft re-bushed
A little lithium grease sprayed on the shaft usually cures it.
A little lithium grease sprayed on the shaft usually cures it.
Melting Slicks
Joined: Mar 2006
Posts: 3,342
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From: Connecticut
Originally Posted by captainmorgan
How do I get the grease on the shaft? Do I have to take the carb apart?
It will take a while to work its way in as you move the throttle back and forth. If you keep moving the throttle back and forth now it will load the intake up with fuel so just drive it for a while and it will work its way in
Like I said, I have seen this problem with re-bushed Qjets .... you may have another problem with the linkage but it certainly will not hurt to lubricate the throttle shaft.
Team Owner
Joined: Apr 1999
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Originally Posted by captainmorgan
How do I get the grease on the shaft? Do I have to take the carb apart?
What he is talking about on quadrajets is 20 years of use and the throttle shaft bores waring out. your problem is probably choke related
Last edited by gkull; Oct 2, 2006 at 03:17 PM.
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From: Minnesota
Originally Posted by gkull
Do you have some kind of choke system holding it open for a fast idle?
What he is talking about on quadrajets is 20 years of use and the trottle shaft bores waring out. your problem is probably choke related
What he is talking about on quadrajets is 20 years of use and the trottle shaft bores waring out. your problem is probably choke related
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From: Minnesota
Originally Posted by 73jst4fun
Did you check first to see the carb is free moving and the linkage/butterflies are not hanging up, then I would check the cable, sounds like it may be clamped down too tight or just worn out...jmo
Le Mans Master
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From: cincinnati ohio
St. Jude Donor '09
I'll bet you have the throttle blades about as far closed as possible, right?
I have two 650 Speed demons on my blown smallblock and the front carb does the same thing.
It seems that the engine vacuum will pull the primary throttle blades open just enough to increase the idle. like you say if you snap throttle it comes back. I even cut a slot and move the shaft spring to a tighter spot.
Spraying a good penetrent/lube around the throttle shaft along with a pretty hefty return spring has just about made it right
I have two 650 Speed demons on my blown smallblock and the front carb does the same thing.
It seems that the engine vacuum will pull the primary throttle blades open just enough to increase the idle. like you say if you snap throttle it comes back. I even cut a slot and move the shaft spring to a tighter spot.
Spraying a good penetrent/lube around the throttle shaft along with a pretty hefty return spring has just about made it right
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From: Minnesota
Originally Posted by yellow 72
I'll bet you have the throttle blades about as far closed as possible, right?
I have two 650 Speed demons on my blown smallblock and the front carb does the same thing.
It seems that the engine vacuum will pull the primary throttle blades open just enough to increase the idle. like you say if you snap throttle it comes back. I even cut a slot and move the shaft spring to a tighter spot.
Spraying a good penetrent/lube around the throttle shaft along with a pretty hefty return spring has just about made it right
I have two 650 Speed demons on my blown smallblock and the front carb does the same thing.
It seems that the engine vacuum will pull the primary throttle blades open just enough to increase the idle. like you say if you snap throttle it comes back. I even cut a slot and move the shaft spring to a tighter spot.
Spraying a good penetrent/lube around the throttle shaft along with a pretty hefty return spring has just about made it right
Race Director
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
something is not right i would be looking at the linkage cabling...if Lars set it up its hard to imagine its the carb
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Instructor
Joined: Dec 2004
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From: Gainesville GA
Originally Posted by conway62
My Demon 750 does the same thing. It is only a year old. Last year it was fine. This year it sticks. I will be interested to see what you find.
If your carburetor ran perfectly fine for a year, and then the problem started you most likely have some dirt or debris causing the linkage to bind. First make sure there isn't any dirt on your accelerator pump arms, from there thoroughly clean the linkage parts, and spray down with a good lubricant like CRC or WD-40.
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From: Minnesota
Originally Posted by Doug S
Does the engine return to the lower idle speed if you shut the car off, and restart it, or only if you snap the throttle?
Thanks
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From: Minnesota
Originally Posted by Doug S
Does the engine return to the lower idle speed if you shut the car off, and restart it, or only if you snap the throttle?
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From: cincinnati ohio
St. Jude Donor '09
I'm waiting for this reply as well. Like I say one of mine does the same thing. It's as if the engine vacuum itself pulls the throttle blades open a bit. I can push the linkage back on mine, but once opened again it sticks open about 200 - 300 rpm more. Shut the motor down and it closes.When the carb is on the bench, the throttle snaps back perfectly.
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From: Minnesota
Originally Posted by yellow 72
I'm waiting for this reply as well. Like I say one of mine does the same thing. It's as if the engine vacuum itself pulls the throttle blades open a bit. I can push the linkage back on mine, but once opened again it sticks open about 200 - 300 rpm more. Shut the motor down and it closes.When the carb is on the bench, the throttle snaps back perfectly.