Another Q-jet question

[vetteboy86]

Since you folks were so good to me last time, I thought I might ask another question. When i was having trouble with the tension spring on the secondary air valves, I just took a wire and wired them shut. For kicks I took the car for a ride, and it seemed to run alot better. I didn't have the bad bog upon acceleration. I fixed the tension spring and set it to what I think it should be. However the car is bogging again. It runs fine under idle, and easy driving. However when you get the RPM's over 3k or so it falls on it's face. When I had the secondary air valves closed, it pulled hard way past this mark. Now is it possible that whoever rebuilt my carb put the wrong size metering rods in. I was talking to a local guy and he said there is no adjustment on that linkage that controls the metering rods. He said you can either bend the linkage, or put some foil under it to act like a restriction, and effectivly make them shorter in theory.Well I just figured somebody could help me once again.

Thanks again

Craig

 

[MMM]

I suggest you get Doug Roe's book on Rochester Carbs. The seconday side of the Quadrajet is adjustable in the following ways:
- Spring tension on the secondary valves
- the height at which the secondary rods sit into the fixed secondary jets
- the secondary metering rods themselves.

The Secondary Rod hanger has a letter designation on it that translates to the distance from the flat mounting surface to the holes that hold the secondary rods. This seats the rods either further in or further out of the secondary jets. The further in, the more delayed the fuel flow as compared to the opening of the secondary air valves.
The rods come in many shapes and sizes, earlier rods have two distinct "steps", later rod have 3. The tip of the rod controls flow at WOT, but the earlier stages control flow through transition.
All of this is explained in Roe's book. I love Q-Jets and have built many for high performance. The biggest difference in a Q-Jet and a Holley (for application) is the Q-Jet requires more vacuum to operate correctly. But then Q-Jets don't leak fuel as badly as Holley's (which start fires). However Rochester even had the low vacuum situation covered. In the 442 W-30's, the manual transmission cars had a 324 degree cam. Built up very little vacuum. So Rochester built these carbs without a primary power piston and primary rods. They just used small primary jets. Some believe they used 2GC jets, but this is not true as the 2GC used taper seat jets and the Q-Jet used flat seat jets.
I have all the original Delco - Rochester books on their carbs. If you e-mail me your carb model number, I can tell you which jets, rods, secondary hanger and tension spring wind up was specified by GM.
One last suggestion. Try advancing the distributor. Sometimes this works wonders for eliminating bog.