Chevrolet: 1971 Nova 350 backfires, vacuum advance, btdc

Question
Roger, I have a 1971 Nova, 350 4 speed. It starts fine, but when I rev the engine a little it will backfire through the mufflers. When I start from a standing stop it runs fine until about half-way through second gear and then it backfires and falls on its face, If I then clutch it and hit it harder it begins to run normal for about half a block and then the same backfire and stumble.

I have replaced the dist. cap, rotor, points, condenser, coil, checked all plug wires and coil wire for proper resistance, checked the plugs, they were OK, reset timing 4 degrees BTDC with vacuum advance line plugged and have set the points.

I did a complete restore on the engine bay about 6 or 7 years ago. It has been running great until 3 weeks ago. I have maybe 6 or 7 thousand miles on a re-build.

Next on my list is the vacuum advance and a carb kit for the Q-Jet.

Any other ideas or thoughts appreciated.
Thanks,
Terry

Answer
Terry;
Hea- I had a lot of trouble with q-jets, till I put a 750 .d..p / or 800 dp on it , but I did play with the quad and I had some good runs with it, I squatered the jets and I replaced the metering rods to a larger size.look for a book or for info on q-jets and replace the jets squater them for instance a 73 on the r/f and a 75 on the l/f and    do the same in the back. replace the metering rods, also make shure the choke is working right that might be your trouble.if you re do the carb make it a manual secondary not vacume.vacume secondarys  suck real bad