Reply to "Engine back-fire"

As for the backfire. Like was mentioned, a standard Holley after a backfire will damage the powervalve. (So you may wanna replace that). There is a anti-blowback piece you can install in the baseplate, that some of the "hotrod" stores like SummitRacing have.

Typically the backfire is a lean condition, so, for starters make sure that your initial setup is correct with the throttle and primary pump. (meaning if thats not giving a proper squirt thats a problem. You are opening the primaries for a shot of air w/o a good shot of fuel). Check to make sure that the "upside down" bolt on the throttle assembly is just-touching the pump lever under the front bowl. When you manually move the throttle you should get a good squirt of fuel. (and while I ramble, if you pulled your plug wires 2x check the order again. I've swapped 2adjacent wires, motor ran, and it did backfire)

First question/answer has a question that comes with it. Do you know if the timing chain has been replaced. Reason is, I'm thinking in 74' it was advanced offset 4degrees. Ultimately you wanna get about 34-36degrees full advance no matter what. (so its all relative). Some folks run around 8-10 initial advance to start with. Set it down there, and see if it at least moves upwards thru the rpm range to, lets say 3000.

On the A/C question. Sure, replace with the 134A if possible, MAKE SURE you get it totally converted and evacuated. The oils that are used with R12 and 134A are not compatable and will damage your system.

Good luck.....Bob