Quadrajet Adjustment: 79 400

Jolo

Jolo

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My quadrajet has pegs where the needle screws are generally. The car is running rich. I know some of these carbs had plugs and are not adjustable and some require a special tool to adjust them. Anyone know what came on these 78 and 79 400 4 speed Trans ams?
 
Are these pegs plastic?
I guess there is no slot on these pegs?
Any chance you can post a picture?
The mixture screws only effect idle mixture.
 
Round metal pins with no screw driver slots. No plastic caps I’ll get a photo
 
Not great photos but you can see the rod. I just can’t see if there is a hex or torx at the base of the rod for an adjustment tool
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I believe they did put caps on idle mixture screws in 70's, but you could remove.
If mixture is too rich off idle, you will need smaller jets or other adjustments.
 
Mine do not have flat spots. Completely round. The special adjusting tool has several tips but not sure the tool will work on my carb.
 
Jolo said:
Mine do not have flat spots. Completely round. The special adjusting tool has several tips but not sure the tool will work on my carb.
Click to expand...
Read this article. It appears those screws have to be removed and replaced with a slotted mixture screw.

Quadrajet idle mixture screw cap removal

Quadrajet idle mixture screw cap removal
cliffshighperformance.com
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Thanks, I suspected that is what I have. I’ll keep an eye on my new spark plugs. The old plugs had carbon deposits but I have no idea how long they were in there or how the car was driven. I do smell fuel when it’s idling so it is probably running a little rich.
 
What plugs did you install and did you gap them?
Did you check the timing?
You smell fuel, you mean raw gasoline or exhaust?
No gasoline leaks?
You checked cap, rotor, and plug wire resistance?
 
New distributor, timing spot on, no gas leaks. the last owner installed a new cat and exhaust but the exhaust smells rich.
 
Jolo said:
New distributor, timing spot on, no gas leaks. the last owner installed a new cat and exhaust but the exhaust smells rich.
Click to expand...
Guessing W72 ran rich from factory. Rich helps get much more then 220 HP rating, if you can believe drag racing estimated ratings.
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The engine had to pass emissions so originally did not run rich.
Needle and seat could be worn or dirty permitting float level to be high but over the internet just guessing.
 
melsg5 said:
The engine had to pass emissions so originally did not run rich.
Needle and seat could be worn or dirty permitting float level to be high but over the internet just guessing.
Click to expand...
Or someone changed jets and/or rods, or put a non original quadrajet on it with higher cfm rating.
 
I do recall that my 78 400 had a strong lacquer odor. The dealer told me the cat caused the odor. This might be normal considering these cars don’t have all of today’s emissions controls.
 
Jolo said:
I do recall that my 78 400 had a strong lacquer odor. The dealer told me the cat caused the odor. This might be normal considering these cars don’t have all of today’s emissions controls.
Click to expand...
Back in the day dropped pellets out of cat on 78 Grand Am...just kidding that is/was not PC.
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L J said:
Or someone changed jets and/or rods, or put a non original quadrajet on it with higher cfm rating.
Click to expand...
If they did that they wouldn't have left non-adjustable mixture screws.
 
L J said:
I guess your not aware many quadrajets had hardened caps on idle mixture screws, so not worth trouble.

Quadrajet idle mixture screw cap removal

Quadrajet idle mixture screw cap removal
cliffshighperformance.com
Click to expand...
The cap has been removed exposing the screws that are round and have no slot for a screwdriver, look at the pictures in post 4 when you enlarge them.
 
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