about 3 days ago i finished putting my vortec heads on my trans am. i got everything all buttoned up, took it for a ride, and everything was fine while cruising. so i decided to open her up a little bit, and see how much better these heads were than my old 624's. the instant the secondaries opened, the revs went down, it decelerated, and backfired several times. it seems to me that the secondaries are opening and letting air in, but no fuel. the carb is a holley 600 with vacuum secondaries with approximately 800 miles on it. originally i thought that somehow something in the fuel transfer tube was clogged and not letting fuel in the secondary bowl, because i changed primary jets and i had a hard time getting the fuel transfer tube back in place. however, i took a fuel bowl screw out, and it was full of gas. the carb was running fine when i took it off a month ago, so i have no idea what to do. thanks in advance for your help.

 

Hmmm...you took the carb off a month ago. Sounds like it dried out and you may have got some deposits forming in passages or some of the gaskets may have shrunk.

At this point it would probably be best to haul the whole thing apart and give it a thorough cleaning. Carbs that dry out can often get a white flaky deposit in the float bowl. Clogs things up nicely. Try and get the Red or Blue " No stick" gaskets. They resist drying out better than the regular " Brown " gaskets.