Let me preface this by saying I'm no expert and fumbling thru my QJets as well.
In park, the primaries will wind the motor up just fine. therefore, the air valve(butterflies on top locked out by vaccum) will never open. If you drove down the steet with no hood or air cleaner you would see them gradually open by vaccum release, this allows the secondaries to step in instead of dumping . When the vac. can is fully released, the position is dictated by secondary air speed vs. air valve spring tension.
Just reread your post and saw that you said the butterflies were opening, so disregard. Hold open the air valve with your finger(engine off but at operating temp. and ensure that the secondary butterflies are operating. My friend had an old truck with a QJet but his grandfather had tapped the secondary pin for the choke lockout so that even when the choke had moved the lever away they would not open.
I havent been able to get the secondaries on my 85 tuned. Had the same problem with my other Qjet that I currently have on my 73(no rebuild). I did swap over my secondary vac. can, rods and hangers. When I put the old carb on the 73, I put some junkyard parts on it just so It would run. Took it for a test drive and it feels like my wifes GTO!! Never adjusted spring tension on the old one but I am going to figure out what it is and transfer all the old carbs secondary parts and settings over to the 85's carb to eliminate the carb as a variable. The only other difference is 35's on the 85 running in Drive(should be essentiqally same as 73's TH350) and the 73 has 33's. I have adjusted tension on the 85 and it got much better, however, I could go past best(still unsatisfactory) and hear the engine turn lean.
If your carb is a 49 state emissions stock 1986, it likely will have a dual capacity accal pump. It will be a 90 degree connector on the top-front-pass. side of carb. I am not well versed in this 'cause I havent had one but know if its just the pump and not a CCC cali carb then its still good and modifiable.
Sorry for the novel, but I figure that your question stemmed from poor performance and mayb e this wiil lead you in thr right direction. Your local library might have Doug Roe or Cliff Ruggles book on Rochester Quadrajets and they are both excellent resources.
Good Luck
