Idle speed doesn't return to idle.
Thread Starter
Senior Member since 1492
Joined: Aug 2000
Posts: 87,936
Likes: 156
From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Idle speed doesn't return to idle.
This is the exact opposite of the problem I had with my Holley 3310-750. This is a brand new Holley 4150 HP Pro Series. Installed today and after accellerating to 40mph, and then coming to a stop the idle speed doesn't return to 850. Instead it'll stop at 1200 or 1100 or sometimes 1500rpm's. 
After about 10-20 seconds without the car moving the idle speed will return to 850.
Do I need a stronger throttle return spring?
Thanks
Len
After about 10-20 seconds without the car moving the idle speed will return to 850.Do I need a stronger throttle return spring?
Thanks
Len
Thread Starter
Senior Member since 1492
Joined: Aug 2000
Posts: 87,936
Likes: 156
From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Originally Posted by CGGorman
Running way rich?
Thread Starter
Senior Member since 1492
Joined: Aug 2000
Posts: 87,936
Likes: 156
From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
I know very little about Holley's. Can a rich mixture cause the idle to remain high?
Le Mans Master
Joined: Oct 2000
Posts: 8,897
Likes: 1,357
From: Santa Ana CA
Make sure that the secondary linkage is not hanging up. At one time I put a microswitch under the secondary linkage to active an alternator cut-out. This then held the linkage up, just slightly and caused the same problem you describe.
Melting Slicks
Joined: Jun 2002
Posts: 2,844
Likes: 99
From: Orrtanna Pa.
When I was recurving my distributer I tried a few different kits,and the Summit kit with the light springs installed did the same. The advance wouldn't pull back all the time,causing the idle to wander a bit.
Advanced
Joined: Jun 2004
Posts: 89
Likes: 0
From: St. Charles IL
Originally Posted by Jughead
I know very little about Holley's. Can a rich mixture cause the idle to remain high?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Whenever I have had this problem ( I have it right now as a matter of fact ) it has been a small vacuum leak, I am gioing to fix mine tommorrow I know it a headlight actuator.
You can test if it's a vaccum line by blocking the line off and drive it around. If not a line, cheick the base gasket, you did use a new one with the new carb like you are supposed too I am sure because a different base carb will make a different impression in the gasket and cause a leak.
Make sure the carb is bolted to the right torque and if you still haven't found the leak after all that well have fun
You can test if it's a vaccum line by blocking the line off and drive it around. If not a line, cheick the base gasket, you did use a new one with the new carb like you are supposed too I am sure because a different base carb will make a different impression in the gasket and cause a leak.
Make sure the carb is bolted to the right torque and if you still haven't found the leak after all that well have fun
Melting Slicks
Joined: Nov 2003
Posts: 2,668
Likes: 119
From: St. Charles Mo
CI 5 & 8 Veteran
Originally Posted by jyounane
Might be worth checking that the throttle linkage is not interfering with the base of the air cleaner.....happened to me once....but with a quadrajet.
Good luck...Joe
Good luck...Joe
Also check the secondary throttle plates to make sure they are not hanging up slightly open. I have seen them hang up because the carb was not centered on the intake or the intake/carb gasket.Bullshark
Thread Starter
Senior Member since 1492
Joined: Aug 2000
Posts: 87,936
Likes: 156
From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Thanks for the fast replies guys. I'll check the list above out.
I checked the jets on this carb before I installed it and all 4 jets are 82's. Isn't that a bit large?
I checked the jets on this carb before I installed it and all 4 jets are 82's. Isn't that a bit large?
Thread Starter
Senior Member since 1492
Joined: Aug 2000
Posts: 87,936
Likes: 156
From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Originally Posted by MotorHead
You can test if it's a vaccum line by blocking the line off and drive it around. If not a line, cheick the base gasket, you did use a new one with the new carb like you are supposed too I am sure because a different base carb will make a different impression in the gasket and cause a leak.
Make sure the carb is bolted to the right torque and if you still haven't found the leak after all that well have fun
Make sure the carb is bolted to the right torque and if you still haven't found the leak after all that well have fun
I torqued the carb base as per Holley....110 in/lb
Melting Slicks
Joined: Dec 2000
Posts: 2,198
Likes: 2
From: Eastern Connecticut
Originally Posted by Jughead
I checked the jets on this carb before I installed it and all 4 jets are 82's. Isn't that a bit large?
Safety Car
Joined: Jun 2004
Posts: 4,652
Likes: 80
From: Lakeland Florida
Idle Speed
I had a similar problem with the revs staying at 1500 RPM
My problem turned out to be with the secondary linkage. It did not return to the normal position, or let the butterflies stay open more than normal. After playing with the linkage, and moving some hoses around from underneath this area, maybe the vacuum advance hose and others, I got rid of the problem.
My first check was with all the vacuum hoses and connections. That is what several people told me the symptoms sounded like. And that is how I found the linkage problem.
Good luck
kdf 1973 454
kdf 1986 L98
My problem turned out to be with the secondary linkage. It did not return to the normal position, or let the butterflies stay open more than normal. After playing with the linkage, and moving some hoses around from underneath this area, maybe the vacuum advance hose and others, I got rid of the problem.
My first check was with all the vacuum hoses and connections. That is what several people told me the symptoms sounded like. And that is how I found the linkage problem.
Good luck
kdf 1973 454
kdf 1986 L98
Thread Starter
Senior Member since 1492
Joined: Aug 2000
Posts: 87,936
Likes: 156
From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Funny thing I noticed. I'm running a side exhaust and right on the concrete, below where the exhaust outlet is, there's a light deposit of carbon. Now here's the funny thing, the right(pass side) has more of a deposit than the left(drivers) side.
Thread Starter
Senior Member since 1492
Joined: Aug 2000
Posts: 87,936
Likes: 156
From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Originally Posted by The Money Pit
When I was recurving my distributer I tried a few different kits,and the Summit kit with the light springs installed did the same. The advance wouldn't pull back all the time,causing the idle to wander a bit.
Not sure it's dist related. I didn't have this problem with the dist and the 350 it was in.
Man, always something with these cars. Fix one thing and a new problem arises.
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I just fixed the exact same problem today, found out one of the seals on one of my hedlight acuators was bad, I blocked off that line now my engine returns to normal idle speed like it is supposed to. 
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
Jughead same problems here. Tried the vacuum issues and found it wasn't the cause. I should have listened to LARS and put on that holley heat shield I ordered from Summit. Problem was I destroyed it becuase I do not have the correct tools, specialty vise is needed and bent it all to crap trying to clear the pump shot arms. Basically my BG requires two 90 degree bends to clear the pump arms in front and in back and no BG does not make a heat shield so I'm stuck with what I got. So when my engine gets hot while sitting at a light with low idle and very little cooling air flow from the fan the heat comes up off the manifold and boils the fuel in the primary float and the RPM raises from 850 to 1200. When cold the idle is perfect. I really need to go down to the grage and figure out how to rebend that plate correctly and install it. Problem is the bends I made will show and it looks like junk. Blew $35 for nothing!
Here is LARS instructions, sorry I don't have the time for uploading the the pictures so I hope you can pcture this in your mind or give me your e-mail and i'll forward you his document.
BG and Holley carbs need a reflective heat shield installed under the carb: The accelerator pump wells are close enough to the hot manifold that the fuel in the pump wells will boil after hot engine shutdown. As the fuel boils and vaporizes, it pushes fuel out the accel discharge nozzles, flooding the engine after shutdown. Holley builds a shield, but it does not fit correctly. Seen here is a modified Holley shield: I have trimmed about an inch off the forward edge so it will clear the thermostat housing. The rear edge has been trimmed forward. The right side of the shield has been cut inwards to prevent the throttle shafts from binding on the shield. The right corners have been trimmed at a 45-degree angle to clear the carb inlet line. Finally, the shield has been bent downwards and “jogged” so that the accel pump levers will not hit the shield: If you install a flat shield, the accel pump levers will hit the shield, and will be partially depressed. This will cause an off-idle flat spot and stumble. In order for the “jogged” shield to clear the base gasket, the gasket “ears” must be trimmed. Shown here is a trimmed base gasket that will allow the bent shield to fit properly.
Shields can be made in many ways. Shown her is the custom shield that I use on my own car. It’s fabricated from a piece of aluminum sheet stock. Note forward and rear edges bent down to clear accel pump levers.
Here is LARS instructions, sorry I don't have the time for uploading the the pictures so I hope you can pcture this in your mind or give me your e-mail and i'll forward you his document.
BG and Holley carbs need a reflective heat shield installed under the carb: The accelerator pump wells are close enough to the hot manifold that the fuel in the pump wells will boil after hot engine shutdown. As the fuel boils and vaporizes, it pushes fuel out the accel discharge nozzles, flooding the engine after shutdown. Holley builds a shield, but it does not fit correctly. Seen here is a modified Holley shield: I have trimmed about an inch off the forward edge so it will clear the thermostat housing. The rear edge has been trimmed forward. The right side of the shield has been cut inwards to prevent the throttle shafts from binding on the shield. The right corners have been trimmed at a 45-degree angle to clear the carb inlet line. Finally, the shield has been bent downwards and “jogged” so that the accel pump levers will not hit the shield: If you install a flat shield, the accel pump levers will hit the shield, and will be partially depressed. This will cause an off-idle flat spot and stumble. In order for the “jogged” shield to clear the base gasket, the gasket “ears” must be trimmed. Shown here is a trimmed base gasket that will allow the bent shield to fit properly.
Shields can be made in many ways. Shown her is the custom shield that I use on my own car. It’s fabricated from a piece of aluminum sheet stock. Note forward and rear edges bent down to clear accel pump levers.