backfire through carby

hi i am in australia i have a 351 windsor i changed my sump gasket and pulled oil pump drive out , since putting all back together i have a misfire , the car is backfiring through the carby under load , the timing is set about 10 bftdc as it was before , but i just cant get rid of this misfire , the car still pulls ok but just slight popping through carby , i know i may have put the dizzy in a tooth out but have checked and reset timing with no1 at tdc any suggestions


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Double check the firing order.
Maybe you have a bad intake valve?