Carb Adjustment
- Thread starter matthud
- Start date
4 barrell what?
I will assume you mean a Quadrajet carburetor. Remove the air cleaner. Look for where the throttle linkage attaches to the carb (driver's side). On the carb, it will be like a little "ear". Look behind the ear and you'll see a standard head screw on a horizontal plane-passing through a small spring. Move the throttle open a couple of times and you'll see how it rests against this screw. You'll need a small tipped screwdriver and approach from the front, turn clockwise to raise engine speed.
Suggest you check ignition timing (distributor vacuum disconnected), and also check/replace the PCV valve-confirm it is the proper application, I believe AC CV36-I can confirm later if you need to know-books at home. This affects idle as well. Ideally, use a vacuum gauge and adjust your idle mixture crews.
if it is a Holley, it's very similar only the screw is on a vertical plane. Again, the "ear" and you'll see the screw between the front and rear barrells.
Carter and Edelbrock will also be similar. Just wiggle the throttle a few times and you'll see the screw. Piece 'o' cake...
Rick
I will assume you mean a Quadrajet carburetor. Remove the air cleaner. Look for where the throttle linkage attaches to the carb (driver's side). On the carb, it will be like a little "ear". Look behind the ear and you'll see a standard head screw on a horizontal plane-passing through a small spring. Move the throttle open a couple of times and you'll see how it rests against this screw. You'll need a small tipped screwdriver and approach from the front, turn clockwise to raise engine speed.
Suggest you check ignition timing (distributor vacuum disconnected), and also check/replace the PCV valve-confirm it is the proper application, I believe AC CV36-I can confirm later if you need to know-books at home. This affects idle as well. Ideally, use a vacuum gauge and adjust your idle mixture crews.
if it is a Holley, it's very similar only the screw is on a vertical plane. Again, the "ear" and you'll see the screw between the front and rear barrells.
Carter and Edelbrock will also be similar. Just wiggle the throttle a few times and you'll see the screw. Piece 'o' cake...
Rick
P
photovette
Guest
While you're post, how do I properly adjust the choke and fast idle speed--QuadraJet? Thanks!
Choke and fast idle
I see you have a '77, w/ Q-jet. Is yours a divorced (thermostatic coil w/ rod) choke or the little round "can" on the side?
Here, I will guess it is a divorced choke. First, make sure the choke pull-off works correctly. You'll need a vacuum tool-MityVac or other. You can do all this on a warm engine.
You'll also need the specifications. Suggest the GM Service Manual or you can purchase a carb kit to get the spec sheet and rebuild the carb another time. A carb kit spec sheet will also give you a nice picture of the carb and identify certain bits. Disconnect the thermostatic coil rod from the carb. Next, open the throttle, close the choke plate completely and release the throttle. I assume you know what/where the fast-idle cam is. Slowly push down on the "ear" of the cam until it clicks to the second step. A rule of thumb is a 3/16" drill bit should just pass nicely between the choke plate and the front/side wall of the carb throat. Next, use the MityVac to open the choke pull-off. Measure the choke plate opening again. 17/32" comes to mind here but I could be wrong.
The fast idle screw is below the fast idle cam. Reconnect vacuum line to choke pull-off. Since the car may be warm, and the choke is already situated on the second step of the fast idle cam, start the car and use a 8" or so long regular small tip screwdriver to reach in under the cam and get to a small screw located real close to the secondary lock out tang. High idle should be about 1500 RPM. The spec sheet will tell you, also.
I have made a few assumptions here regarding your familiarity with Q-jets but it really is not too difficult and will allow you to properly "bond" with your machine.
Take your time, look it over and get familiar with where everything is and you'll impress your friends and amaze your enemies. Good luck.
Rick
I see you have a '77, w/ Q-jet. Is yours a divorced (thermostatic coil w/ rod) choke or the little round "can" on the side?
Here, I will guess it is a divorced choke. First, make sure the choke pull-off works correctly. You'll need a vacuum tool-MityVac or other. You can do all this on a warm engine.
You'll also need the specifications. Suggest the GM Service Manual or you can purchase a carb kit to get the spec sheet and rebuild the carb another time. A carb kit spec sheet will also give you a nice picture of the carb and identify certain bits. Disconnect the thermostatic coil rod from the carb. Next, open the throttle, close the choke plate completely and release the throttle. I assume you know what/where the fast-idle cam is. Slowly push down on the "ear" of the cam until it clicks to the second step. A rule of thumb is a 3/16" drill bit should just pass nicely between the choke plate and the front/side wall of the carb throat. Next, use the MityVac to open the choke pull-off. Measure the choke plate opening again. 17/32" comes to mind here but I could be wrong.
The fast idle screw is below the fast idle cam. Reconnect vacuum line to choke pull-off. Since the car may be warm, and the choke is already situated on the second step of the fast idle cam, start the car and use a 8" or so long regular small tip screwdriver to reach in under the cam and get to a small screw located real close to the secondary lock out tang. High idle should be about 1500 RPM. The spec sheet will tell you, also.
I have made a few assumptions here regarding your familiarity with Q-jets but it really is not too difficult and will allow you to properly "bond" with your machine.
Take your time, look it over and get familiar with where everything is and you'll impress your friends and amaze your enemies. Good luck.
Rick
Fractionally challenged
Sorry, folks, I was a little off:
This should give both Matthud and photovette a good start-
The first adjustment (choke rod) is 3/32" vs. 3/16".
The second (choke pull-off) is 17/64" vs. 17/32".
PCV valves as follows (AC Delco):
1969 350/427 4 bbl.: CV 736C 427 3X2 bbl.: CV746C
1977 350 4bbl./std. trans. CV 774C 350 4bbl. auto. trans. CV775C
All the best.
Rick
Sorry, folks, I was a little off:
This should give both Matthud and photovette a good start-
The first adjustment (choke rod) is 3/32" vs. 3/16".
The second (choke pull-off) is 17/64" vs. 17/32".
PCV valves as follows (AC Delco):
1969 350/427 4 bbl.: CV 736C 427 3X2 bbl.: CV746C
1977 350 4bbl./std. trans. CV 774C 350 4bbl. auto. trans. CV775C
All the best.
Rick
Similar threads
Corvette Forums
Supporting Vendors
Dealers:
