fast idle/curb idle on Rochester 2GV

Hey guys - trying to dial things in and really struggling to understand how to set the fast idle/curb idle screw. There is only one screw on the throttle linkage side and the picture was taken while engine is warm, choke is open, idle is about 850 (bounces around but I'm assuming it's due to cheap timing light). If that screw is not touching anything (and this is also how it was set before I rebuilt the carb), how is it impacting anything?

If I tighten it down, I get higher rpm but then interferes with choke linkage.

I'm really feeling like to woke up on the short bus with this.

I've read that I need to blip the throttle and the cam will drop, but I'm not seeing any change in the cam. Is it supposed to drop about 90 degrees clockwise?

Thanks for any guidance

Oh - vacuum is about 18 inches Hg if that matters, solenoid "A" on bottom left pushes plunger out as engine warms, is there an adjustment to be made on the solenoid/plunger?

Second picture us labelled so that might help with explanations

Thanks Double Dingo - I watched that video a couple of times and it didn't really tell me how to adjust - but i guess the screw just contacts the cam and then as the choke opens it moves the cam which then rotates under the screw and allows for the throttle/idle to drop to curb idle?

I adjusted with this in mind and it seemed to work.

When the engine is cold, and you fully depress the throttle to set the choke, does the cam set like it's supposed to? If so, yes, the screw holds the idle faster until the engine warms up and the choke opens, then the cam will rotate off the screw with opening choke. I hope I explained that correctly.

Is it possible that your choke is working fine but you have a hefty vacuum leak? Like are all vacuum ports plugged? That’s one thing to check when the idle screw can’t get your idle down far enough.

Edit: just realized what I’m looking at: the fast idle (or smog/anti diesel) solenoid is holding your throttle open. You adjust that by taking a wrench and turning the hex head of the solenoid plunger. Righty tighty.

DoubleDingo said:

When the engine is cold, and you fully depress the throttle to set the choke, does the cam set like it's supposed to? If so, yes, the screw holds the idle faster until the engine warms up and the choke opens, then the cam will rotate off the screw with opening choke. I hope I explained that correctly.

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Yes, what you described is what happens.

Trucksareforwork said:

Is it possible that your choke is working fine but you have a hefty vacuum leak? Like are all vacuum ports plugged? That’s one thing to check when the idle screw can’t get your idle down far enough.

Edit: just realized what I’m looking at: the fast idle (or smog/anti diesel) solenoid is holding your throttle open. You adjust that by taking a wrench and turning the hex head of the solenoid plunger. Righty tighty.

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Should I adjust the solenoid plunger? Push idle up a bit?

Rotten 1 said:

Should I adjust the solenoid plunger? Push idle up a bit?

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I don’t know your setup. For instance, in the mid 80s, A stock automatic c10 V8 would idle somewhere around 550-600 rpm in drive. You are reporting 850 warm, which sounds high for a stock motor (a cammed motor needs more idle). Some GM engines were set up so that the solenoid is actually the idle screw, so that when the key is turned off, the solenoid de energizes and closes the throttle plate to avoid dieseling.

If the solenoid is your idle screw, and you have a stock motor, I would think you want lower idle not higher.

What’s your setup? I assume with the 2 barrel you are in either an older truck or a v6.

Trucksareforwork said:

I don’t know your setup. For instance, in the mid 80s, A stock automatic c10 V8 would idle somewhere around 550-600 rpm in drive. You are reporting 850 warm, which sounds high for a stock motor (a cammed motor needs more idle). Some GM engines were set up so that the solenoid is actually the idle screw, so that when the key is turned off, the solenoid de energizes and closes the throttle plate to avoid dieseling.

If the solenoid is your idle screw, and you have a stock motor, I would think you want lower idle not higher.

What’s your setup? I assume with the 2 barrel you are in either an older truck or a v6.

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1974 C10 with 350 V8. Previous owner replaced plugs, wires and HEI. I rebuilt carb 2 months ago. She runs but I’m trying to find out if there is a sweet spot for tuning.

Rotten 1 said:

1974 C10 with 350 V8. Previous owner replaced plugs, wires and HEI. I rebuilt carb 2 months ago. She runs but I’m trying to find out if there is a sweet spot for tuning.

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Finding the sweet spot to me would be to check and set timing, then set your hot idle and adjust idle mixture (and reset idle to your target in the process), then set high idle with choke engaged.

You’d want you use your vacuum gauge for setting mixture.

Better men than me can tell you best way to do it.

I think idle spec for your engine setup is probably 600-700. Remember if you have an automatic trans that’s in drive (not park).

Trucksareforwork said:

Finding the sweet spot to me would be to check and set timing, then set your hot idle and adjust idle mixture (and reset idle to your target in the process), then set high idle with choke engaged.

You’d want you use your vacuum gauge for setting mixture.

Better men than me can tell you best way to do it.

I think idle spec for your engine setup is probably 600-700. Remember if you have an automatic trans that’s in drive (not park).

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Thanks, timing is currently 8 degrees BTDC, next weekend I will probably figure it out and see how 10-12 degrees works

Rotten 1 said:

Thanks, timing is currently 8 degrees BTDC, next weekend I will probably figure it out and see how 10-12 degrees works

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great. be sure your vacuum advance is disconnected when you are setting timing. (not to be condescending...happens all the time).

Trucksareforwork said:

great. be sure your vacuum advance is disconnected when you are setting timing. (not to be condescending...happens all the time).

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No offense taken - that is exactly the kind of mistake I would make. Thanks!