ok so i got a job and i built a mustang for a guy got the block bored .30 over and new performer intake spacer comp cams big mutha thumpr cam and here is my problem....he wanted to keep the stock heads couldent see himself spending 1300 dollars on a set of afr......dumb i know but yeah i built the motor but kept the stock rockers changed springs lifters and the pushrods but now i got it all together its all timed up right and i keep getting backfires its not starting either if anyone has any input i would really appriciate it..what i am thinking is it could be that he needs to buy new rockers but i dont know never kept stock rockers or heads on my builds. thx......oh and to introduce the car its a 93 lx originaly a 4 cyl but 302 now .30 over stock heads (i ported and polished them.)mutha thumper cam performer intake spacer relocation bracket no ac no smog if somone has input it would b appriciated....and i know i have horrable literature. thx