70 GTO & Holley carb dies around turns or braking - Pontiac GTO Forum
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post #1 of 7 (permalink) Old 02-04-2016, 09:21 AM Thread Starter
 
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70 GTO & Holley carb dies around turns or braking

I have this 70 GTO that has a 400 in it and a Holley CARB number R84014-1

Unknown modifications except headers and sounds like an upgraded cam.

It dies out or stumbles sometimes around turns or braking.

Before I started messing with it the mixture screw on one side was 1/2 turn out and the other side was 1 turn out.

I have a vacuum gauge on it and is reading 11 in park and about 7-8 in gear. In gear the RPM is about 700
..
If I turn both mixture screws all the way in it makes no difference in RPM or vacuum and car keeps running. Same thing if I back it out 1 1/2 turns.

Where do I start on diagnosing this problem and or tuning.

Thanks again
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post #2 of 7 (permalink) Old 02-04-2016, 10:29 AM
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Spray some carb spray around the base of the carb and where the butterfly shafts go through and see if the idle changes.
Sounds like it is sucking air somewhere.
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post #3 of 7 (permalink) Old 02-04-2016, 03:10 PM Thread Starter
 
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I sprayed everything I could think of and get to with no change in the idle.

Intake manifold, carb mounting base, other carb gaskets, All the vacuum lines and tees-connections I could see, PCV, power brake booster fitting etc.

I really don't know anything about Holley's except all posts say for this carburetor is get rid of it ASAP guess it was a bad carb.
Which I can't do right now.
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post #4 of 7 (permalink) Old 02-04-2016, 05:25 PM
 
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Go on the Holley website and wtch the video on setting float levels in the carb..

Stalling on turns and braking may indicate that the float level is wrong, and therefore stalls it under those conditions.

Is your throttle plate opened a little? Must be pulling some mixture thru that idle circuit if when screws are all the way in it is not stalling..

Remember the mixture screws provide a volume of air and gas....the mixture..

Open is more of the mixture..closed is less...when you crack the throttle plate with the screw it passes only air, but because of the velocity it pulls some more mixture as well....

Maybe the needle tips of the mixture screws are messed up from screwing them in too hard by someone.....

If the throttle plate is fully closed and float level right...you sure be able to get it to run on 1 and 1/2 turned out on those mixture screws...

But I defer to the great carb gods...I am not one....check that float...

And of course we are talking of fully warmed up operation...chokes are a whole nuther matter

Stay with it
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post #5 of 7 (permalink) Old 02-04-2016, 05:28 PM
 
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Losing that throttle plate a little may increase your Vacumn as well...those are low readings and throttle plate effects them....
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post #6 of 7 (permalink) Old 02-04-2016, 05:48 PM
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What Lemans guy said about your float levels. First thing I would check.
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post #7 of 7 (permalink) Old 02-08-2016, 06:14 PM
 
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If the jetting is to big the idle screws can act like what you describe. The low vacuum at idle is an issue, what kind of intake is on the engine?

1964 400 4 speed Roller cammed RoadRacer
1969 400 T400 auto 2nd owner
2004 LS1 6 speed modded for roadracing
1966 GTO Altered wheelbase former 1970s show car
1973 Challenger 360/727
1931 Ford Model A
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