Carb Adjustment - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**BanjoDude** · 07-09-2023, 07:37 PM

Well...I thought I was doing a good thing and adjusted the carbs after refreshing the ignition (points, condenser, cap, rotor, wires - plugs on order). However, I clearly don't know what I'm doing, because while it runs like a top when I first start it, it's a bear to start after it's warm. I've double checked timing, and that's dead on, so I'm thinking it must have been messing with the carb that did it. It ran great before I did that... I suppose no good deed goes unpunished. Any tips on how to better adjust things? It's a stock 2 barrel on a 307 in my 69 C20. Thanks! -Wes

**davischevy** · 07-09-2023, 08:04 PM

What adjustments did you make to the carb?

geezer#99 · 07-09-2023, 08:10 PM

And what’s your timing set at besides being dead on?

**BanjoDude** · 07-09-2023, 08:48 PM

I have dwell set to 30 and timing at 2 BTDC. I watched several videos (maybe my first mistake) which said I should run both screws all the way in, and then back them out until it runs rough, then back in a half turn. I can't remember the specifics, but that was the gist of it. I should have counted turns so that I could have returned it to where it was...

Casper42 · 07-09-2023, 09:07 PM

I hadn't heard of that method, but I've done well with turn both all the way in then turn both out exactly 3 turns out...can adjust slightly from there, like perhaps 2.5 turns out equally. just my $0.02

geezer#99 · 07-09-2023, 09:10 PM

Bump your timing up to 12 degrees. Check your dwell after you do.
That will increase your idle. Turn it back down to minimum. About 500-600 rpm.
Procedure for mixture screw adjustment is set both at 1 and 1/2 turns out from lightly seated. Then adjust for highest vacuum reading. Turn them in first until idle drops. Try to keep them equal. Go small adjustments.
And don’t forget to plug off the vacuum advance when setting timing.

**ghackett1** · 07-10-2023, 07:25 AM

Quote:

Originally Posted by geezer#99

bump your timing up to 12 degrees. Check your dwell after you do.
That will increase your idle. Turn it back down to minimum. About 500-600 rpm.
Procedure for mixture screw adjustment is set both at 1 and 1/2 turns out from lightly seated. Then adjust for highest vacuum reading. Turn them in first until idle drops. Try to keep them equal. Go small adjustments.
And don’t forget to plug off the vacuum advance when setting timing.

…ditto…

**BanjoDude** · 07-10-2023, 09:27 AM

Quote:

Originally Posted by geezer#99

Bump your timing up to 12 degrees. Check your dwell after you do.
That will increase your idle. Turn it back down to minimum. About 500-600 rpm.
Procedure for mixture screw adjustment is set both at 1 and 1/2 turns out from lightly seated. Then adjust for highest vacuum reading. Turn them in first until idle drops. Try to keep them equal. Go small adjustments.
And don’t forget to plug off the vacuum advance when setting timing.

Thank you! I'll give this a shot.

geezer#99 · 07-10-2023, 10:00 AM

Just remember the old saying!
Timing first, carb second!

**davischevy** · 07-10-2023, 10:38 AM

I may have missed it, but disconnect your vacuum advance before setting timing.

54blackhornet · 07-10-2023, 01:21 PM

I have a 2GV divorced choke on my 71 C/20. I had it rebuilt by a knowledgeable guy in Philly. It took multiple tries to get it set up properly. Both of the idle mixture screws are out two turns from bottom. You have to be sure engine is warmed up and completely off choke. Get it to idle then adjust mixture screws for best idle and vacuum.

**BanjoDude** · 07-14-2023, 04:39 PM

I finally had a chance to adjust to 12 degrees and reset the carbs. It runs so much better now. Thanks!

07-09-2023, 07:37 PM	#1
BanjoDude Junior Member Join Date: Feb 2023 Location: Fletcher, OH Posts: 77	Carb Adjustment Well...I thought I was doing a good thing and adjusted the carbs after refreshing the ignition (points, condenser, cap, rotor, wires - plugs on order). However, I clearly don't know what I'm doing, because while it runs like a top when I first start it, it's a bear to start after it's warm. I've double checked timing, and that's dead on, so I'm thinking it must have been messing with the carb that did it. It ran great before I did that... I suppose no good deed goes unpunished. Any tips on how to better adjust things? It's a stock 2 barrel on a 307 in my 69 C20. Thanks! -Wes __________________ Found Grandpa's old '69 Chevy C-20 - It'll never leave the family again. "For just a little more, you can do it yourself!"

07-09-2023, 08:04 PM	#2
davischevy Senior Member Join Date: Sep 2008 Location: Harrison, Arkansas Posts: 9,787	Re: Carb Adjustment What adjustments did you make to the carb? __________________ other Larry Build thread, Arkansas K10 https://67-72chevytrucks.com/vboard/...=755797&page=5 The ability to speak several languages is an asset, but the ability to keep your mouth shut in any language is priceless.

07-09-2023, 08:10 PM	#3
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,520	Re: Carb Adjustment And what’s your timing set at besides being dead on?

07-09-2023, 08:48 PM	#4
BanjoDude Junior Member Join Date: Feb 2023 Location: Fletcher, OH Posts: 77	Re: Carb Adjustment I have dwell set to 30 and timing at 2 BTDC. I watched several videos (maybe my first mistake) which said I should run both screws all the way in, and then back them out until it runs rough, then back in a half turn. I can't remember the specifics, but that was the gist of it. I should have counted turns so that I could have returned it to where it was... __________________ Found Grandpa's old '69 Chevy C-20 - It'll never leave the family again. "For just a little more, you can do it yourself!"

07-09-2023, 09:07 PM	#5
Casper42 Registered User Join Date: Nov 2022 Location: Seattle, WA Posts: 312	Re: Carb Adjustment I hadn't heard of that method, but I've done well with turn both all the way in then turn both out exactly 3 turns out...can adjust slightly from there, like perhaps 2.5 turns out equally. just my $0.02 __________________ '72 C10 Cheyenne SWB North Carolina truck for 50 years, 72k original miles, Medium/Hawaiian Blue, 3 owners - one for 40 years, garaged kept, original: sheetmetal, undercarriage, moldings, glass * * * New - engine rebuild at 65k in 2015, one repaint in 2010, new front bumper, houndstooth seat, carpet, 8 inch rally wheels on 275-60R-15, LED lighting. - Semper Paratus!

07-09-2023, 09:10 PM	#6
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,520	Re: Carb Adjustment Bump your timing up to 12 degrees. Check your dwell after you do. That will increase your idle. Turn it back down to minimum. About 500-600 rpm. Procedure for mixture screw adjustment is set both at 1 and 1/2 turns out from lightly seated. Then adjust for highest vacuum reading. Turn them in first until idle drops. Try to keep them equal. Go small adjustments. And don’t forget to plug off the vacuum advance when setting timing.

07-10-2023, 10:00 AM	#9
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,520	Re: Carb Adjustment Just remember the old saying! Timing first, carb second!

07-10-2023, 10:38 AM	#10
davischevy Senior Member Join Date: Sep 2008 Location: Harrison, Arkansas Posts: 9,787	Re: Carb Adjustment I may have missed it, but disconnect your vacuum advance before setting timing. __________________ other Larry Build thread, Arkansas K10 https://67-72chevytrucks.com/vboard/...=755797&page=5 The ability to speak several languages is an asset, but the ability to keep your mouth shut in any language is priceless.

07-10-2023, 01:21 PM	#11
54blackhornet Registered User Join Date: Jul 2008 Location: Eastern Oregon Posts: 2,266	Re: Carb Adjustment I have a 2GV divorced choke on my 71 C/20. I had it rebuilt by a knowledgeable guy in Philly. It took multiple tries to get it set up properly. Both of the idle mixture screws are out two turns from bottom. You have to be sure engine is warmed up and completely off choke. Get it to idle then adjust mixture screws for best idle and vacuum. __________________ 71 C-20 07 Magnum RT AWD

07-14-2023, 04:39 PM	#12
BanjoDude Junior Member Join Date: Feb 2023 Location: Fletcher, OH Posts: 77	Re: Carb Adjustment I finally had a chance to adjust to 12 degrees and reset the carbs. It runs so much better now. Thanks! __________________ Found Grandpa's old '69 Chevy C-20 - It'll never leave the family again. "For just a little more, you can do it yourself!"



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