Ever since I have gotten my car it has had no power on the top end. If I go full throttle at about 3500-4000 it just falls on its face. If I keep in it it will either backfire out the exhaust or through the carb, and just keep doing it. I have had some people tell me its valvesprings and some day ignition problems. I could kinda see how either one would make sense. My car has an Accel HEI if that makes any difference. What do you guys think?

 

I would start with simple stuff like checking timing, check plugs/wires, etc. Has the camshaft ever been replaced? I've seen where a camshaft with a worn lobe or 2 will cause backfire up through the carb, like it's spitting at you, when you rev it up.

 

Timing is already set. Have replaced the plugs but not the wires. The engine is pretty old and worn, it was rebuilt at some point so I will assume the cam has been replaced, but not positive. I will be replacing the 350 with a big block in the next few months so if its anything too serious I wont really worry about it.

 

Sounds like 'valve float' to me - springs or lifters, but could also be wires!!
If it gets worse when it's raining, it's the wires.
If that fixes it, fine - if not, take it easy 'til the BB's ready!!