Crank but wont start

I bought the mower not running. Its a 46" cut craftsman. It has the 25hp v-twink intek motor. It cranks, kinda trys to start but wont. It does kinda pop when trying to start. Thought might be timing issue so replaced flywheel key but did not help. Has clean new gas, i cleaned the carb, replaced fuel pump. I have checked kill switches, has new battery. Can anyone help me figure this darn thing out please