For anyone that's been following the saga of my 68 CST troubles, here's a quick update...
Symptom: Backfire through the carb on initial throttle and under a moderate to heavy load. No backfire at all once the initial blip of the throttle is over with. Sounds fine at idle, 2000k, and 3500k.
Basically, it acts like a big ol' vacuum leak or completely hosed timing, but I'll be damned if I can figure it out. At one point I reported that I heard a strange noise, but I'm almost certain now that it is/was a combination of exhaust leak on the passenger side and/or the heat riser was acting flaky.
I just had the carb (Q-Jet) rebuilt by a reputable guy, put it on this evening, and while you can tell he did a whole lot of good, the root cause of my problem still hasn't been identified.
After I threw the carb on and reset the idle, I played with the timing (I was/am at 8 degrees and tried it at about 4 and 12), but that didn't make a lick of difference. I also tried moving the vacuum advance from the port on the carb to the manifold. That didn't make a dent, either.
Guess it's time to tow the old girl over to The Professional and let him figure it out since I'm running out of patience, time, and good weather. Damn!
