Holley Carburetor - Cold Start Fast Idle Adjustment

Does your car carbureted car have trouble idling on cold mornings? Hidden on the passenger side of most four barrel carburetors is a second idle adjustment called the fast idle. This is located behind the electric choke on Holley carburetors and is only accessible if you manually open the throttle. The fast idle screw adjusts your idle RPM when the car is cold and the choke is activated which can prevent the car from stalling. This is different from the curb idle screw which adjusts the idle when the car when the choke is off. Ideally, the fast idle should be set to about 1200 RPM to allow the car to warm up and go into gear without stalling on a cold morning. The carburetor in this video is a Holley 80457 and is 600 CFM. This is a 1986 Chevy C10 with air ride suspension.

[ClassicCarsComics]

Doing the Lord’s work! I needed to know where the curb idle was and this is just what I needed! Camaro is back up and running right now.

[WAL_DC-B]

A small ignition wrench can also be used on the fast idle screw if it's difficult to access with a screwdriver.

[MystikalDawn]

1/4 SAE wrench works too, my 670 street avengers screw is always exposed (kind of) so I don't need to hit the throttle to make the screw visible.

[Nizzwell]

Nice dude, just done mine on my 79 c10 shortbed great vid kool truck 👊

[ari.]

The red plastic cam on my holley 670 gets stuck in the top part. Has to be pushed down manually

[Martyn]

im havikg a diffirent rno sound issue. it sound like a very high pitch tone and regardless of whixh way i adjust the screws. i can tell a different spund comes int play while adjusting the screws and it occurs right on cold start . i had also boticed one of thr air hoses gad came off by mistake but im not feelimg air suction or air going out so im guessing its clogged. any wild guesses or suggestions?

[faronf]

I own a 84 f-150 with a 4 barrel 4180c carb . I set up the choke perfect for cold start, don't see no binding issues etc . The cold engine fires up good but once warmed up, there is no way that the choke will kick off the last step on the fast idle cam, no matter how much I back off the fast idle screw ??

The only way is for the choke to come off the last step on the fast idle cam, is by pushing the cam lever manually . Then having to adjust the choke thermostat for a warm engine . All is good until the engine cools off & now the choke plate is open too much .

I was wondering if it could be a possible bad choke spring ?

[Thesuppcabinet]

Got my electric choke dialed just right, but I had no high idle with choke on. I adjusted my high idle screw and bam sounds just right on a cold start, but it will not kick down and return to normal idle when I blip the throttle. Any suggestions??

[mikeyoungblood]

Is there a certain number of RPMs the fast idle screw will drop or increase based on a 1/4 turn of the screw? Not sure how far to turn it..

[DoyleFM]

I have three old carburetor trucks that run like crap when they're cold. While I think I probably have some vaccum issues, all three will start up fairly easily. Two have rebuilt carburetors on them but all three act the same.
They typically start up pretty much immediately but then start skipping & smoking badly. I can't tell if the smoke is rich or lean on any of them but they tend to smooth out, for the most part, once they start getting warmed up.
They're 1979 2.3L Ford, 1982 1.9L Mazda & 1983 2.4L Nissan engines.
Do you have any suggestions, based on this limited information, 😁 as to what might be going on with them? I'm in the humid southeastern United States.
Thanks!
🇺🇸

[aaronhatfield]

how are you supposed to adjust this without dumping a ton of fuel into the engine?

[kitkatftw]

My issue is that the throttle blip will NOT make it come down to curb idle setting, i'm super stumped

[ari.]

What rpm you running on drive? 550 or 600?