problems with backfiring
i had a 421 sbc built about a year ago. i had it built turnkey including dyno time for tuning and breaking it in. well on the dyno everything was fine and a couple days ago i finally completed my truck so put the engine in and attempted to fire it. im using a msd digital 7 part number 7531. i have not hooked a computer up to the digital 7 yet so im using all defualt setting. im also using no cam sync.
my problem is when the motor attempts to fire it will backfire and flame up through the carb. it does it everytime. what could be wrong. ive check the firing order a dozen times and made shure it corresponds to the plugs. the cap was marked my my engine builder with a #1 so i assumed that was #1 plug. my timing on my dyno sheets says that total timign was 36*. the defualt from the digital 7 start retard is 10*. is this taking out too much timing? does the msd have to be programmed prior or will the defualt settings work? please help