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Don
Buffalo

USA
54 Posts

Posted - 18 Sep 2016 :  10:14:36 PM  Show Profile  Reply with Quote
I just installed a dual quad set up on my 65 389 gto stock engine it has 10-1 comp the carbs are 400cfm from a 340ci buick engine. They have been rebuilt to stock condition and are on a offy manifold i have a 2004r trans 2200stall converter and 355 rear end. My problem is when it shifts from first to second there is a boug in fact when it is cold it almosts quits. I have richened the choke adj the acel pump arm adj the carbs to no avail. I finally advanced the timing that helped alittle but the boug is still there at times Can anyone give me any direction as to where i go from here? I have taken the progressive throttle linkage off the front carb so i'm running on the rear carb only untill i can correct the problem so i don't think the problem is in that carb.
Thanks Don

tjs44
Cochise

USA
412 Posts

Posted - 19 Sep 2016 :  10:08:01 AM  Show Profile  Reply with Quote
They are way too small for the 389.You cant figure CFM as 800 for a dual quad setup.Pontiac used a pair of 750s on their 421 SD engines with the tunnel ram.A pair of factory early 60s pontiac AFBs are perfect on a 389.Tom
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Blued and Painted
Chief PONTIAC

USA
3405 Posts

Posted - 19 Sep 2016 :  10:57:24 AM  Show Profile  Reply with Quote
The cfm is OK. I'm not saying the calibration is spot on but cfm would only make a difference in the upper rpm range
Your not getting enough pump shot when the throttle/s are opened. The pump circuit is not staying primed or there is a pressure leak past the check valve/ball.
If the carb is bead blasted or had water set in the bowl, the check ball seats need re-forming and ethanol resistant pumps must be used.
Call or email Mr. cliff for good advice and parts.
-- http://www.cliffshighperformance.com/ --


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.

Edited by - Blued and Painted on 19 Sep 2016 10:59:12 AM
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tjs44
Cochise

USA
412 Posts

Posted - 19 Sep 2016 :  11:07:10 AM  Show Profile  Reply with Quote
Cliff is not a dual quad guy!Get ahold of Jon Hargrove at the carburator shop.He is the AFB and dual quad guy.Tom
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Phil
The Great White Buffalo

USA
7215 Posts

Posted - 20 Sep 2016 :  12:42:26 AM  Show Profile  Reply with Quote
X2!

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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Don
Buffalo

USA
54 Posts

Posted - 21 Sep 2016 :  2:21:32 PM  Show Profile  Reply with Quote
Chchise
Do you have a web site or no for the carb shop?
Don
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tjs44
Cochise

USA
412 Posts

Posted - 21 Sep 2016 :  8:34:24 PM  Show Profile  Reply with Quote
You might contact whoever did the combo for you.The 400s should drive fine on the street if setup right but a pair of stock pontiacs would have been better IMO.I have used many of the buick factory dual quad 401 carbs over the years with no issues.Might just need some more tuning.Tom
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67drake
Sitting Duck

Azerbaijan
1501 Posts

Posted - 22 Sep 2016 :  08:19:37 AM  Show Profile  Reply with Quote
Don,I don't have a web address for him,but his phone # is 573 392-7378. I just talked to him a few weeks ago myself.


71' GTO Original 400 M20 3.23 posi
13.95@102.1 MPH on street tires
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Phil
The Great White Buffalo

USA
7215 Posts

Posted - 23 Sep 2016 :  12:46:44 AM  Show Profile  Reply with Quote
www.thecarburetorshop.com

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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