okay first of all I would like thank all of you for the many of questions you will be helping me with now lets get to it I have a briggs and stratton 5hp side shaft motor model# 135212-0129-01 im am putting the fuel tank and carb from a 5hp briggs and stratton side shaft motor model# 135202-0153-02 iam getting fire to the plug and fuel to the carb but all im getting in return is backfiring from the carb and the exhaust any help would be greatly appreaciated thanks

 

100% sure the keys not sheared off in the flywheel which would throw off the timing?
100% sure the floats not stuck in the carburetor causing it to flood?

 

Do a compression test and or take plug out and see if both valves are seating. I just did a vertical shaft engine and it would try to fire but would pop through carb,,pulled head and the Intake valve seat is out and holding valve open.