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Holley Carb high idle

Abe Jauregui

Newbie
Joined
Apr 21, 2021
Messages
79
Loc.
Los Angeles
Ok, I have a 70 bronco with a 600 cfm Holley truck avenger electric choke. It drives like a dream and starts up great. My issue is when its warmed up and driving for a while when I downshift to neutral at a red light and come to a stop, it feel like the choke is getting stuck and its revving high at 1500-1800. I have to give it a quick blip on the gas peddle to get it to rise then come down to 850-900 idle. I checked the timing, the ground and 12 volts to the coil. electric choke is good when it's cold by opening then closing at start up from 1500 down to 850-900. Should I be tinkering with the curb idle screw? again when its warmed up, in neutral it idles fine. This is only when downshifting to a stop does the revs stay at 1500 all the way unless i blip the throttle. Appreciate any help. This forum has helped me so much.
 

Lawndart

Sr. Member
Joined
Nov 23, 2014
Messages
754
Loc.
66031
I would not mess with the idle initially.
Take a close look at the choke linkage and see if there is anything interfering with operation. Mine did a similar thing when I installed my Holley and the linkage was just slightly rubbing on the carb base gasket (were the gasket extends ever so slightly out from the carb and the manifold). A slight trim and never had the problem again.
 

m_m70

Contributor
Sr. Member
Joined
Jun 14, 2001
Messages
1,056
Loc.
Pacifica, CA
yup, look at the linkage for any rubbing/binding.
I had this issue once and a stronger return spring was needed.
you may want to drive it around, pull over when it's reving high without blipping idle down and open hood to look at linkage and see where it's hanging up.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
43,772
All of the above for sure.
And how old is the carburetor?
How clean is the carburetor?
Have you ever cleaned and lubed the linkage?

Sometimes after years of use they simply need a good cleaning and light lubricating with some WD-40 or similar.
You typically don’t want a gummy lubricant because it will leave the gummy even when it dries out and then it will get sticky again.
A light lubricant like WD doesn’t last very long, but if the linkage is sound, not worn and doesn’t get dirty very quickly, it can remain functioning properly for a year or more before you have to do it again.

And are you guessing at these RPM levels? Or do you have a tachometer?
Just wondering because 850 to 900 RPM is a pretty high idle.
We were talking about this just last week and if you need it that high, or want it that high, it’s fine. But a normal idle is 650 to 700 for a stock, or stock like cam.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
43,772
Can't view anything. It's asking me to "sign in" and/or to update my browser with all sorts of options.
Any other way to make it viewable?

Paul
 

B RON CO

Contributor
Bronco Guru
Joined
Jun 29, 2016
Messages
2,334
Hi, a better way to install a return spring is get a kit from Holley, two springs and a bracket, and pull the lever with the large hole forward. The bracket mounts on the front carb mounting bolt.Your return spring is not doing the job. Google Holley return springs. Good luck
 
OP
OP
Abe Jauregui

Abe Jauregui

Newbie
Joined
Apr 21, 2021
Messages
79
Loc.
Los Angeles

1970 Palmer

Full Member
Joined
Mar 2, 2020
Messages
406
I would not be able to sleep at night knowing I spent $50 to $75 for a simple spring bracket. Nothing is wrong with the OE return spring/bracket.
 

B RON CO

Contributor
Bronco Guru
Joined
Jun 29, 2016
Messages
2,334
Hi, Holley had a Mr. Gasket #9678 throttle return spring kit which would work for you. Good luck
 

4xfun

New Member
Joined
May 16, 2005
Messages
48
Maybe it just the view, but that may not be the correct spring. It is still stretched and looks like it has been modified to reach. You may also need a stronger spring.
 

desertoasis2b

Contributor
Jr. Member
Joined
May 18, 2007
Messages
110
you may need to adjust the fast idle screw, it is on the back side of the choke. if you have your installation manual it is on page 9 if not you can google it. you need the engine off then advance the throttle wide open to access the 1/4 inch screw then back it off just slightly and retest.
 

1970 Palmer

Full Member
Joined
Mar 2, 2020
Messages
406
Your problem is that you have a handful of mismatched parts. It's easy to run into these issues when you bolt on aftermarket parts designed for a wide range of applications, not made for a specific vehicle.

Take a closer look at the return spring, and also the angle the spring pulls against the throttle shaft. The way you have it currently, the spring has no mechanical advantage to pull the throttle shaft closed. That spring should not require that it be bent at all to properly connect if everything is correct.
 
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OP
Abe Jauregui

Abe Jauregui

Newbie
Joined
Apr 21, 2021
Messages
79
Loc.
Los Angeles
Your problem is that you have a handful of mismatched parts. It's easy to run into these issues when you bolt on aftermarket parts designed for a wide range of applications, not made for a specific vehicle.

Take a closer look at the return spring, and also the angle the spring pulls against the throttle shaft. The way you have it currently, the spring has no mechanical advantage to pull the throttle shaft closed. That spring should not require that it be bent at all to properly connect if everything is correct.
Is there a set up you can show me that would best work? I’m replacing that spring or might get one of the set ups the other members have suggested
 

1970 Palmer

Full Member
Joined
Mar 2, 2020
Messages
406
Is there a set up you can show me that would best work? I’m replacing that spring or might get one of the set ups the other members have suggested
Look at the end of the throttle shaft as a clock face. Your return spring is pulling the throttle shaft at close to 3:00 o'clock. If you look at a OE spring position it's closer to Noon to 1:00 o'clock against the throttle shaft. It's not the tension of the spring, it's the geometry and angle it's pulling. If you have ever driven a car with a very heavy throttle return spring it's a PITA.
 
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