Okay, before anyone tries to negate my use of a Q-Jet, please be tolerant and accept my infatuation with them. That being said...
Well, I've become very familiar with Q-Jets over the past few years, rebuilding, adjusting, collecting jets and secondary rods etc. So far, I've only run into a few stinkers. Last year, before I finished the 350 for my firebird, I purchased a 795 cfm, electric choke Q-jet from an '85 454 Chevy truck. I received it and promptly rebuilt it. I matched up all the gaskets and such, and put it back together. I got it on the car, and at idle and partial throttle it ran great. A little rich, but that's okay. I figured I'd tune it out of it later. Well, the time came to dip into the secondaries, and.... nothing, just a lot of popping and hesitating. Assuming an incredibly lean bog, I readjusted the air door, and put some richer secondary rods in. Went for the secondaries again and nothing. So, I pulled 'er back apart, and couldn't find anything wrong. Curiosity got to me and I changed the throttle plate to main body gasket, to see what that would do. Well, I sure had secondaries now, and was able to get it tuned okay. However, I could never tune the incredible richness out of the idle. The sun of a gun pulled great on the top end, but there was a part idle hesitation, and was always running rich at idle. I tried everything! Even bottoming out the idle adjustment screws didn't do squat. Then one time I lifted up the secondary hangers to get a better look at what letter they were, and the car about died. That's when I found out it was pulling out of the secondary wells at idle. A little more messing around, and I figured out why my idle always changed after changing secondary rods. I've never run into this, and no one in my area can give me a reason. The only two gaskets that were in the kit gave me the option of no secondaries, or full-time secondaries. If someone else has run into this problem or has and idea what might remedy it, I'd be greatly appreciative.
p.s. sorry for the novel, I just thought I'd be thorough