I am trying to figure out which secondary power valve I need. The only information I can find is for the primary power valve, I think. Looking up the factory specs it says that I should have a 6.5 primary and an 8.5 secondary. This carb is a stock 4053 on my 69 302. Just trying to get it dialed in for the elevation here, about 5,500 ft.. Idle vac. is 7", don't know the cruise vac. at this time. I have 68 primary and 72 secondary jets in it right now. Seems to run a little rich but with 66 primary jets it stumbles a little upon acceleration at any speed. So I think I have the correct primary jets installed. I am open to all advice on jetting, power valve etc. for this altitude.
Try adjusting both accelerator pumps first by backing out the nut above the spring just a little at a time. You might have a little slop in that linkage causing the pump squirter not to "hit" as quick as it should.
Basic rule of thumb is to reduce jet sizes one size for every 2000 ft elevation so I would reduce your jets by 3 sizes.
On the Primary PV, whatever your vacuum reading is then divide that in half...you said you had 7" so then I would install a 3.5 PV.
On the secondary side I would plug the PV and then increase the jet size by 7-10 sizes to compensate.
I think the factory jet sizes on your carb were 68 pri and 76 sec. so after reducing according to altitude I come up with 65 & 73. If you remove the secondary PV and plug the hole then you would want to increase the sec. jets to somewhere between 80-83.