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quadrajet idle speed adjustment

greggome

Active member
Joined
Jul 25, 2014
Messages
38
Location
florida
Corvette
1968 corvette bronze coupe
My 68 327 has a referbed quadrajet on it. My mechanic had this thing set to idle at 600 rpm. I want to adjust it to idle at the proper 750 rpm. I understand there are 2 idle speed screws, the base idle screw and the fast idle screw. I'm familiar with Holley carbs but the quadrajet is confusing. How do i set the proper idle on this carb?
 
Last edited:

LLC5

Well-known member
Joined
Sep 28, 2004
Messages
2,299
Location
Wa.
Corvette
98 black 6spd convert.
My 68 327 has a referbed quadrajet on it. My mechanic had this thing set to idle at 600 rpm. I want to adjust it to idle at the proper 750 rpm. I understand there are 2 idle speed screws, the base idle screw and the fast idle screw. I'm familiar with Holley carbs but the quadrajet is confusing. How do i set the proper idle on this carb?



The base idle set speed screw is on the left side of the carb (driver side) and the two fuel mixture screws are at the front of the base plate. The fast idle set speed screw is on the right (passenger) side by the choke.
 

greggome

Active member
Joined
Jul 25, 2014
Messages
38
Location
florida
Corvette
1968 corvette bronze coupe
Yes I know the location of all the screws on the carb but with 2 different idle screws how do you adjust them to achieve a consistent 750 rpm when motor is warmed up?


The base idle set speed screw is on the left side of the carb (driver side) and the two fuel mixture screws are at the front of the base plate. The fast idle set speed screw is on the right (passenger) side by the choke.
 
Last edited:

Les55

Active member
Joined
Sep 20, 2014
Messages
37
Location
Vallejo California
My 68 327 has a referbed quadrajet on it. My mechanic had this thing set to idle at 600 rpm. I want to adjust it to idle at the proper 750 rpm. I understand there are 2 idle speed screws, the base idle screw and the fast idle screw. I'm familiar with Holley carbs but the quadrajet is confusing. How do i set the proper idle on this carb?
You turn the idle mixture screws in all the way. Then back them out 1 3/4 - 2 turns, both screws.
Start the car. Adjust the idle screw (automatic transmission 650 rpm) (standard transmission 750 rpm).
Then turn the left idle mixture screw out untill highest rpm is achieved. Turn back in (for lean idle adjustment) 1/4 turn.
Adjust idle back to 650 auto/750 standard.
Now adjust right idle mixture screw out to highest rpm. Turn back in (for lean idle adjustment) 1/4 turn.
Reset idle adjustment screw to 650 auto/750 standard transmission.
This is standard for all quadrajet carburetors.

Sent from my SM-G930V using Tapatalk
 

LLC5

Well-known member
Joined
Sep 28, 2004
Messages
2,299
Location
Wa.
Corvette
98 black 6spd convert.
Yes I know the location of all the screws on the carb but with 2 different idle screws how do you adjust them to achieve a consistent 750 rpm when motor is warmed up?


You do not adjust both set screws when the choke is fully open and the engine is hot, the only adjustment for a hot idle setting with the choke completely open is the base idle speed set screw on the left side of the carb.

If you have an electric idle stepper/kicker solenoid (not sure if '68's had them) then you would set the desired idle speed with that solenoid, but first you would disconnect the solenoid and set the base idle lower by about 100 rpm's with the set screw on the throttle linkage, then plug the stepper solenoid back in and set to the desired idle speed using the solenoid.
 

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