Backfiring out carb and wont run right
In no particular order
vacuum leak
carb AFU IE gummy, floats too high / flooding, dirt in needles seats/ pump problems
timing / ignition. Use a piston stop. Check your timing mark. Check that the advance mechanism is working and the timing is where you think
CHECK THE PLUG WIRES
Valve hung open, IE bent valve, damaged valve gear mis adjusted valve, etc