Just when I think I have my carb dialed in, I don't

[Matt69olds]

Get the engine fully warmed up, about a 10 mile drive should have it completely warm. Lightly swat each idle mixture screw, then back them out around 2 turns. Start the engine, pick one mixture screw, and turn it out 1/2 turn, see if the vacuum increases. If so, turn the other out 1/2 turn. Keep going back and forth until you get the highest vacuum. Once it’s maxed out, turn them each in 1/2 turn.

It may take several cold starts to get the choke dialed in. What is the fast idle speed set to? Try setting it to about 1500, good luck!!

if you really want a bolt on, never mess with it again carb, get a Q-Jet from a carb specialist.

 

[SquareRoot]

Buy a holley and you will be very happy. They have a cheaper brand called quick fuel. I replace my edelbrock with a quick fuel and it has been heaven, starts every time.

Buy a Edelbrock Pro-flo 4 and be ecstatic and done with the idiosyncrasies of carbs forever.

 

[88 diesel]

The idle speed will creep up as the engine warms and becomes more efficient. Make sure your vacuum choke pull off is working. Cold first thing the choke should be slightly open after setting. You are doing that right. It sounds like your choke isn't opening properly after starting. As the car warms you need to tap the throttle to move the choke setting screw to the next step. Notice it is cammed to gradually lower the idle speed to its final idle position. Your idle screws will do very little until you are warmed up and off the high idle cam.

 

[Matt69olds]

I don’t think edelbrock carbs have a choke pull off. I remember fiddling with the choke on a old Holley carb I had years ago, only way I could reliably get it to start, warm up on a fast idle, and run right when it was warm is to adjust the choke heater so the flap just BARELY closed. Once the engine was running, the airflow thru the carb, combined with a little slop in the linkage, allowed the choke flap to open enough for the engine to run smoothly.

As I said earlier, if the op wants a bolt on and forget about it carb, a Q-Jet is the only way to go. Think about it, the Q-Jet was factory equipped on millions of GM cars and trucks. No way in hell GM could afford to have warranty issues or complaints about poor drivability or cold start issues. Have it rebuilt and calibrated CORRECTLY, tune it correctly, close the hood and forget about it. It will run better, probably get better mileage, and be trouble free

 

[MisterB]

The idle speed will creep up as the engine warms and becomes more efficient. Make sure your vacuum choke pull off is working. Cold first thing the choke should be slightly open after setting. You are doing that right. It sounds like your choke isn't opening properly after starting. As the car warms you need to tap the throttle to move the choke setting screw to the next step. Notice it is cammed to gradually lower the idle speed to its final idle position. Your idle screws will do very little until you are warmed up and off the high idle cam.

When you say the choke should be slightly open after setting, what do you mean by setting? Pressing the accelerator once or twice?

So went out this morning and started it cold, after the choke adjustments and vacuum gauge adjustments yesterday. Today is much colder than yesterday. There was frost on the entire truck. It took two pumps instead of one to get it started. It fired up and idled better than it has been. It didn't die, but still was stumbling until gradually after a couple minutes, the high idle came up and stayed at the max I set it to.

I'm thinking all the remaining issues are in how the choke is adjusted. When I adjusted the choke yesterday, I did it with the engine stone cold and before I pressed the accelerator. I adjusted it until the flat just barely touched fully closed. Should I have hit the gas pedal once first? Is this stumbling between starting and the first couple of minutes before it idles higher because the choke isn't opening enough?

Also, all this talk about a quadrajet being better. I dunno. I have a quadrajet in my '69. When I moved from 5,400 feet to 2,000 feet, and 85 octane was no longer available and I had to go with 87, I had some of these same issues until it finally got dialed in, and it's been running fine ever since.

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[88 diesel]

I'm going to make an assumption. First carb?
Unlike Fi all carbs are a little different.
There's nothing that says one pump on the gas pedal does it all. There are variables.
A professional carb rebuilder will bench set every carb he does and rarely will two be identical where you could say Rochester requirements are blah. Holley's are blah. There is a starting point listed online I'm sure for every carb made. But there are variables.
By the sounds of it I would try two pumps of the accelerator pedal next time and see if that gets you closer to what you expect. Each time you pump the pedal a stream of raw fuel should be forced into the front two barrels of the carb.
If you post a pic of the carb and if possible the data tag or stamp I'll look it up and try to be more helpful.
Bill

 

[MisterB]

I'm going to make an assumption. First carb?
Unlike Fi all carbs are a little different.
There's nothing that says one pump on the gas pedal does it all. There are variables.
A professional carb rebuilder will bench set every carb he does and rarely will two be identical where you could say Rochester requirements are blah. Holley's are blah. There is a starting point listed online I'm sure for every carb made. But there are variables.
By the sounds of it I would try two pumps of the accelerator pedal next time and see if that gets you closer to what you expect. Each time you pump the pedal a stream of raw fuel should be forced into the front two barrels of the carb.
If you post a pic of the carb and if possible the data tag or stamp I'll look it up and try to be more helpful.
Bill

I'm going to make an assumption. Reading comprehension not your strength? Lol. Didn't see my very last paragraph, where I talked about the quadrajet I had to dial in with my '69?

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[88 diesel]

Yeah I went back and saw it and felt foolish. Some of us take things for granted and my assumption came from the questions you were asking. Didn't mean to offend you. Best of luck.
Bill

 

[MisterB]

Yeah I went back and saw it and felt foolish. Some of us take things for granted and my assumption came from the questions you were asking. Didn't mean to offend you. Best of luck.
Bill

Lol. No problem. I appreciate all your help with this, and would appreciate any help you can give to get me across the finish line.

I totally understand how they are all different and some need one pump, others need 2 or 3. It also depends on how cold it is. I don't think pumping is my problem with it stumbling. It think the choke is my problem. If it stays closed too long, it stumbles. Also, if it stays closed for too long, an extra pump or two when it isn't needed, could cause it to become flooded.

I think I need to dial in how far the choke closes, and so based off what you were saying I'm just wondering if I should adjust the choke AFTER I have pumped the accelerator once or twice when the truck is cold, or does it not even matter if I pump first before adjusting the choke?

I think I need to adjust the choke so it isn't quite as closed, which should allow the carb to breathe and idle better when first starting up, but who the hell knows.

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[MisterB]

I just watched this video on how to adjust the choke on an Edelbrock carb, and they are suggesting you put a credit card here and adjust it until it touches the card, and then tighten it down and remove the credit card. That little extra air gap may very well be why it stumbles while idling at first

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[MisterB]

I just watched this video on how to adjust the choke on an Edelbrock carb, and they are suggesting you put a credit card here and adjust it until it touches the card, and then tighten it down and remove the credit card. That little extra air gap may very well be why it stumbles while idling at first

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[MisterB]

I just watched this video on how to adjust the choke on an Edelbrock carb, and they are suggesting you put a credit card here and adjust it until it touches the card, and then tighten it down and remove the credit card. Not having that little extra air gap may very well be why it stumbles while idling at first

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[MisterB]

I just watched this video on how to adjust the choke on an Edelbrock carb, and they are suggesting you put a credit card here and adjust it until it touches the card, and then tighten it down and remove the credit card. Not having that little extra air gap may very well be why it stumbles while idling at first

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[MisterB]

Not sure why it posted that so many times

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[Frankenchevy]

Have you seen the video about adjusting an Edelbrock carb with a credit card? Might help you get it dialed in.