So heres the story,

I have a 90 Camaro, race built, 355c.i. 253/253 @.050 dur. 560/560 lift 110lsa cam. 210cc Aluminum heads etc. Thing cranks great idles fine and has a great sound but if I try to rev the motor it stumbles right as the carb hits the secondaries. I have to slowly rev the motor or it "hiccups". Ive changed carbs, added a spacer, done everything I can think of. I then decided to be sure it wasnt the timing curve in the distributor and locked the distributor and have it set at 36 degrees. No advance. it revs fast and fine until i hit that perfect spot around 3k rpm or when I blip the throttle back to the secondaries. I now think It could be the GM Ignition box (basically an MSD 6A). It sounds like its popping through the carb and throught the exhaust when the problem occurs. SO i put a timing light on it and found that it is retarding timing when I rev it which is IMPOSSIBLE, Unless the box is bad or there is a problem. Please anyone who has any idea chime in this has been going on around 8 months and I haven't figured it out. in my experience these boxes either work or don't work so I am stumped. Thanks in advance!