3.8 hesitation off idle

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a.graham52

Greasemonkey
Oct 19, 2017
105
27
28
hey guys,

85 olds cutlass, 3.8. whole car is stock with no mods.

just installed a rebuilt carb from J&J to solve my previous idling issues. iv been able to put some miles on the car now and its pretty nice except for just off idle. it will fall on its face, some times worse then others. if you powerbrake the car you can increase load little by little and then it will just fall on its face. almost seems too "precise" to be a carb issue but never the less i contacted J&J and was given some recommendations but nothing has helped. heres what i have done:

verified air bleed valve set to 1.75" from compressed MC solenoid
adjusted idle mixture screws to obtain 30 degrees MC dwell
road tested with no change
adjusted MC solenoid stop for a little richer mixter per j&j - no change
adjusted for a little leaner mixture - no change.
basic things that led up to carb diagnoses have been done like intake gaskets and vacuum leak checked etc

right now im going to slap in a better quality set of plugs and a new coil but i figured i would see what you guys think.
 

a.graham52

Greasemonkey
Oct 19, 2017
105
27
28
try adjusting mixture using the lean stop adjustment. after that they request it gets returned to be evaluated
 

pontiacgp

blank
Mar 31, 2006
29,270
20,391
113
Kitchener, Ontario
try adjusting mixture using the lean stop adjustment. after that they request it gets returned to be evaluated

if you tried adjusting the lean stop, which I have no idea what that is, and it didn't help I'd be sending it back
 

timo22

G-Body Guru
Sep 10, 2012
550
1,072
93
St. Louis,Mo
From my experiences, I would look into the accelerator pump. An engine needs a good shot when you go from idle or cruise circuit to acceleration. With the engine off, look down the carb and give it full throttle. You should see two steady streams of gas. If no stream, either the rubber seal is messed up or maybe the check ball is missing. If you have a steady steam, maybe adjust the pump to come on quicker. There are usually three slots that the pump actuator arm goes into...timo22
 

a.graham52

Greasemonkey
Oct 19, 2017
105
27
28
two steady steams and also swapped out the AP arm for one that has the hole lower, and closer to the carb which is more aggressive then stock. no dice
 

timo22

G-Body Guru
Sep 10, 2012
550
1,072
93
St. Louis,Mo
I'm guessing the old carb just had idling issues and not the bogging issue? If that's the case , I doubt that the ignition shot craps and I w pull return the carb also. Sorry I couldn't be more help...Tim
 

a.graham52

Greasemonkey
Oct 19, 2017
105
27
28
the car never saw the road the the previous carb installed so I'm not 100% sure.

on thing I would like to have ironed out is spark plug gap and timing procedure. I know to unplug 4 prong connector and adjust to 15 degrees btdc, but at what rpms?
 

MrSony

Geezer
Nov 15, 2014
6,793
6,678
113
Des Moines, Iowa
Is there an adjustable part throttle screw? Its the front half of a qjet, so it should have one.
the car never saw the road the the previous carb installed so I'm not 100% sure.

on thing I would like to have ironed out is spark plug gap and timing procedure. I know to unplug 4 prong connector and adjust to 15 degrees btdc, but at what rpms?
usually the lowest that it will idle at. wait till its warm, adjust hot/curb idle all down until it starts to stumble. You might be able to get it down to 500rpm in park. Then go from there. A chiltons/Haynes/chassis manual would tell ya.
 
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