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Old 05-10-2012, 10:12 PM
cadmanof50s's Avatar
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Holley Carb Fast Idle Adjustment

I have installed a newly rebuilt Holley 600 CFM 80457S carb with electric choke on my Small Block Chevy.

Carb runs really well but had to make the usual adjustments, curb idle, etc,.

I'm trying to adjust the choke and fast idle but having difficulty.

Normal startup routine:
When cold, I pump accelerator once for an initial shot of gas through accelerator pump. Then, without touching the pedal, I crank the engine..and it fires and revs at 1800 RPMS...This is a bit high...so I give the accelerator another small pump...and insteading of the idle droping in a graduated steps, the engine RPM immediately drops below 1000 and eventually it stall because it is not warm enough.

My undertsanding is that as the car warms up and the choke slowly releases the Holley carb steps down the fast idle cam in graduated increments. Once fully warm it it reaches curb idle.

Is what I am experience normal? If not what am I doing wrong?
Manual says to adjust fast idle to about 1200-1500 RPM? But which step? the first one? There are five steps in Holley fast idle cam. BTW, the choke is set at it's middle lean/rich setting.

Once the engine is fully warmed, the Holley is solid and runs like a champ. But until 100% warm, I stall at least 2 times before I leave the driveway...a bit aggrevating)

Help and guidance would be appreciated. Thanks!

Vic

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Old 05-11-2012, 01:50 AM
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Unfortunately there is no "set it exactly like this" instructions- you will need to juggle the fast idle speed using the screw shown below and the "choke on duration" to get it where you can let the engine warm up w/o stalling and to be able to drive off w/o stalling while the choke is still partially closed.

Turning the choke cover sets the choke on duration as well as what step the fast idle cam/screw is used. The fast idle step that you use is going to depend on how far the choke cover has to be rotated to get the duration of choke on you need for the engine to warm up enough to drive. Juggling the two will get you where you have a long enough duration, w/sufficient rpm for the engine to remain running.

Click on the image for a pdf of the INSTALLATION, TUNING, AND ADJUSTMENT MANUAL for your carb.

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Old 05-11-2012, 05:23 AM
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Thanks cobalt,

I clearly understand your post, there may be a bit of juggling to get it right.

I guess what I need to know is (and this sounds funny comming from a man in his 50s) what is the correct way to start a cold car with a Holley carb?

One shot of accelerator and then pump?
or
Crank and hold the accelertor in a bit, or pump it slightly.

They both have very different results in terms of what teh initial fast idle will be.

I've been driving fuel injected cars for so long that I forget how we used to do it in the old days....;-)

Vic
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Old 05-11-2012, 09:29 AM
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Key on, press down the pedal to floor once, let off turn the key to start. Sets the choke on high step idle and drops a little fuel in so it starts.
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Old 05-11-2012, 01:02 PM
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The problem with electric chokes is they don't work off of engine temperature. They usually open to fast and close way to soon after shutting the car down.
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Old 05-11-2012, 04:15 PM
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Quote:
Originally Posted by sstock
Key on, press down the pedal to floor once, let off turn the key to start. Sets the choke on high step idle and drops a little fuel in so it starts.
↑X2

The key doesn't actually need to be in the "ON" position, but if you choose to do it that way, be sure to start it immediately because the choke will begin to open as soon as it gets voltage from the key being in the on position, unless you have it wired to only receive voltage after the engine starts.
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Old 05-14-2012, 06:17 AM
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I decided to pull the plastic choke housing off the carb just to inspect it.

I compared it to one from another one of my Holley carbs. The one I pulled off seemed to have a much weaker spring. I put the other, stiffer-spring, housing on the carb and the choke now works as I expected.

The original one was set two or three notches rich, but I have had to set the replacement one at the center mark as the fast idle didn't come off fro 5 minutes or so...!

It looks like it was just a bad choke spring. Or maybe the guys who rebuilt the carb just reused the old one because it looked to be in good shape.

Either way...thanks everyone for your input.

Vic
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