u/No_Panic_5501

Hello everyone I have a quick question I recently had to replace the transmission a $700R in my '02 S10 build it's got a '89 350 small block in it now I happen to go ahead and replace all the gaskets while I had it off and I retimed it I'm at 12° from top dead center I've tripled check quadruple checked all my timing and for some reason I'm still getting a massive amount of backfire through my carb, anyone happen to have any ideas I've tried to fingertest I've tried the valve cover off I keep finding top dead center and time at 12° from there and it's always in the same spot and yet I still keep getting backfired out of my carbs can anyone please help