Here is the setup

383 rebuilt with 906 heads, ported some
comp cam- intake 504 lift / exhaust 514 lift
intake 274 duration at 50 and exhaust 282 at 50
9.5 to 1

new holley 750 vac. secondary carb
m1 intake
tri y headers
MSD 6al with pro billet dist.

timing has been tried from 8* BTDC -16* BTDC at base timing-

Full advance has been set from 30*-38*


starts fine idles nice. revs well- under any load- (foot on brake) give it some gas it backfires through the carb.

the car is gutless, will not burnout- even in water. what gives? what could be the issue?