I have put an edelbrock top end kit on my 2 bolt main 8:1 compression 70's block chevy350. I have a Holly 650cfm double pump carb. First time I took it out it seemed great, strong response when giving it sudden throttle from idle. A few days later it was weak launching, would not break the tires loose. It was maybe 10 degrees warmer. I have timing set 12 BTC, not sure what timing at 2500 is, I have appx 2500 stall converter as well.
I run premium gas
It backfires and stalls if I am not VERY gentle with it. Even at speed, if i give it too much load i can hear it backfiring while rolling down the road at 50mph. Any ideas? Maybe I blew a power valve?

Cam info:

Operating Range 1500-6500 RPM
Duration Advertised 308° Intake/318° Exhaust
Duration @ .050'' 234° Intake/244° Exhaust
Lift @ Valve .488'' Intake/.510'' Exhaust
Lift @ Cam .325'' Intake/.340'' Exhaust
Lobe Separation Angle 112°
Intake Centerline 107°
Intake Timing @ .050"  Open 10° BTDC
Close 44° ABDC
Exhaust Timing @ .050"  Open 59° BBDC
Close 5° ATDC


Head info:

170cc Intake Ports, 64cc Combustion Chambers, 2.020 /1.600 Valves, 1.460 Valve Springs, .575 Max Lift, 3/8 Rocker Studs  

Sounds like ign. system issue, or major vaccum leak. Both should be pretty easy to find.