Hey Guys My 455 GS Stage tribute car came with a Summit 750 vacuum secondary carb. I know its not the best carb for it to get max performance but I'm just in it for a little road fun now. Here's the question when I put the set screw into the mechanical linkage to pop the secondaries quicker --and kick passing gear--I get a big hesitation then go. The car launches from a standstill fine but some feathering is necessary on the petal and the vacuum operation is probably delaying the secondaries. I can't figure out why it bogs or just won't accept the faster opening secondaries? The carb seems very slow in the vacuum operation without the set screw. It you take it from a roll and drop your foot and can actually feel a delay before the secondaries open. Its a low compression 455 with comp cam and I've got the timing moved up quicker and lower RPM per this site. I guess take out the screw and play with the vacuum spring resistance. I got tp put in a order to Summit anyway and I'll pick up the carbs tuning instructions. Any other ideas would be appreciated.
All you need is to change the spring that controls secondary actuation. I suggest you read this pdf, starting at page 12 http://static.summitracing.com/global/images/instructions/sum-carb instr.pdf Bringing the secondaries in too soon, or too late will produce a bog. Buy this spring kit and experiment. http://www.summitracing.com/parts/HLY-20-13/
Thanks once again Larry. I just found the tuning manual that you suggest on Summit's site just before dropping in here. Yes its a bog, (when the screw is inserted) by disruption of the primary mixture as described in the manual. I'm going to look at the float levels then order the spring kit as suggested.
