Herbert, I am guessing since you are dealing with a Quadrajet that the choke is electric or electro mechanical? Have you checked the choke operation once the engine warms up? I have seen electric chokes installed upside down and would close off instead of opening once the engine got warm. It is really hard to diagnose a problem with posts or over the phone. Take the diagnostic step by step and write down what you have already checked. The process of elimination at this point will be our best bet. From what you describe, the condenser could be the cause, but not likely.
Had an ignition problem on a 1970 Trans Am once. Car would not run. Would start and run then immediately backfire and pop once the engine warmed up then die. Try to start it again and all it would do was turn over. Found out we were getting intermittent spark. Replaced the coil, plug wires and spark plugs. Still the same thing. Replaced the points and condenser. Still the same thing. Had the rotor button off two or there times along with the distributor cap. The distributor cap and rotor were fairly new with only a couple thousand limes on them. Couldn't be the cap or rotor? 1/2 a day later and after it got dark we found the problem. The newer distributor cap had a hairline crack in it. The crack would open up after the engine warmed up and let the spark jump to various grounds... the intake manifold, coil bracket, ground strap bolted to the firewall. Definitely not firing the plugs. A fireworks display under the hood! Replaced the cap and rotor...Voila!! FIXED!! Anyway, hope you get what I saying. Keep at it and give us what you've done and all the info you can. At that point we might be able to throw a few more ideas your way on what to check next. Keep us updated!
Tim
