Help!

ok, i have just done a motor swap in a truck. it's a 350 punched .40 over, mild cam, about 10.5:1 compression. it has a holley 600 4 barrel, secondary vacuum, electric choke and a high rise intake. my problem is, in low rpm's(1000-2500) if i stomp the gas pedal, it hesitates and pops or backfires through the carb. the timing is set at 12 degrees without the vacuum advance. im not sure if its the timing, possibly a vacuum leak, or even the intake? i just need some help. i also even thought the power valve may be blown in the carb. its a brand new carb....any help would be appreciated. :banghead:

ok, i have just done a motor swap in a truck. it's a 350 punched .40 over, mild cam, about 10.5:1 compression. it has a holley 600 4 barrel, secondary vacuum, electric choke and a high rise intake. my problem is, in low rpm's(1000-2500) if i stomp the gas pedal, it hesitates and pops or backfires through the carb. the timing is set at 12 degrees without the vacuum advance. im not sure if its the timing, possibly a vacuum leak, or even the intake? i just need some help. i also even thought the power valve may be blown in the carb. its a brand new carb....any help would be appreciated. :banghead:

Are your valves adjusted right? Is your cam degreed? Do you have a plug wire crossed to another plug (say, 1-8-3-4-6-5-7-2)? Could be a vacuum leak in either the intake or carb, or even a bad or not-installed line.