Backfire thru Carb and popping out the Exhaust

Given the work you've already done, popping out the exhaust will probably be due to either a bad sparkplug or wire, a misrouted plug wire or a burnt valve. It is also possible that you have a bad rocker, a worn cam lobe or a burnt piston. First, try touching each exhaust pipe just after starting: an intermittently firing plug or wire will give a noticably cooler pipe and help localize the trouble. Pull the rocker cover on the 'bad' side and watch the valve action for differences- this will show a bent pushrod or bad rocker. Finally, I would run a leak-down test to see which cylinder is bad and how bad it is; this will also tell you if its a valve or piston.

Jack; Thanks for your insight... Again without your help and input alot of owners out there would give up on their cars too soon. This concern is on another car and last night we found the problem; turns to be a sheared distributor gear pin....

Hi., Well I just went through the exact same thing you are describing. I replaced my dist. with a MSD and a new Holley carb. I also had backfire pops and compression coming back up the carb. If it backfires too much back through the carb you may blow a power valve and will have to replace it utherwise gas will just keep pouring into the cylinders.! Also if you have any kind of header leaks the cold air hitting the valves causes a "pop". Also the stock exhaust headers are way too small. Thus the motor can't breath enough which causes backpressure. I put on a set of aftermarket headers from a vendor in California for $200..(which bolt right up to the stock intermediate pipes) and new gaskets and my problem was solved! I also put on larger intermediate pipes and used the stock mufflers. With the MSD and an aluminum intake with a Holley carb, the new headers and larger pipes... really helped the motor breath better and the car runs great. No backfire or compression problems.