Do you have leaking exhaust. I had some pinholes in my headers and thought I had a timing issue.

Sounds like a timing problem. Did you degree the cam in? Usually if it's a timing problem and it backfires through the carb, it is retarded.

sounds like a timing chain off or some valves sticking.

I had the same type of problem, reviewed timing and firing order literaly 100's of times, found I had mixed #7 and #8 wires....Dumb thing was I checked firing order over and over.

I had paid 300 only for the company to degree the comp cams hydraulic roller cam in at D.S.S. The block came complete i just bolted the external things on like heads and intake.

Get a vacum gauge and check for a intake or carb leak. If that dont work double check your valve adjustment, it could be too tight, then get rid of the advance/retard knob, set up the dist with the black spacer and the springs that allow all timing in at 3500. I forget which ones they are. Start motor run it up to 3500 and set full timing at 34*. If you dont have wires crossed that has to work. I assume you have a msd distrib and box. What was the cam degreed in at?

I had the exact same symptoms when I changes my intake manifold. I had removed the old intake one day and covered the top of the motor. The next day, I put the new manifold on. I had pulled the Dist. cap off with the wires attached and set it off to the side. Apparently, condensation formed inside the cap and it was all wet. I looked for the problem for many hours before I turned the cap over and looked inside.

Assuming that your timing is correct, it sounds to me like your valves are too tight. How did you set the valve lash? What type of cam is it? Hydraulic roller , or ????

you can't deg a cam with the head's off, if they said they deg. the cam and then you put the heads on you got robbed.

I don't see why a cam can't be degreed with the heads off. You still have TDC to reference off of. The cam can be advanced or retarded just fine. You can also read when a lifter will start to move. I just can't think of anything that would be missing which would affect the cam timing.