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Carburetor not working right

Why would the secondaries on my carburetor not work. I have a 1986 Chevy Suburban C20. I have checked all the vacuum line and the all seem to be in good shape. I was just going to rebuild the it but didn’t want to if it wasn’t necessary.



It sounds like you have vacuum secondaries. Maybe the vacuum servo is leaking. Maybe vacuum is not going to the servo. A vacuum gauge can really help in this case. Testing the vacuum and the integrity of the servo can avoid a blind rebuild.

Did you check to see if the vacuum brake diaphram for the secondary’s is working?


The secondaries open. There is a bar that connects to the primaries, it’s job is to restrict the opening of the secondaries so that they don’t open too fast. The manifold vacuum pulls the secondaries open. Open the throttle and push down on the secondaries with a screwdriver to check it. They work. Be sure to let the secondaries close before the primaries.

Are you working the carb without the engine running expecting to see the secondaries to open? wont happen.

What symptons lead you to believe the carb is at fault?

There is a secondary lock-out on the choke linkage.

It’s a Quadrajet folks… The secondaries will not open unless a slight vacuum pulls them open. There is a damper over the secondaries something like a choke plate that provides a sort of constant velocity function. Defeating this turns these fine carbs into the dreaded “Quadrabog”.

From idle, warm engine, snap the throttle wide open and watch the secondary top plate. It should just begin to open before you are forced to close the throttle as the engine nears red-line rpm…That top plate should open very easily with just your finger.

If you STILL don’t think it’s opening, remove the air cleaner and take it out on the road and floor it. In a second or two, you will hear the building roar as the secondaries open.