Likely no spark or no fuel. You dont know if you are getting any fuel,
remove air filter and squirt gas or starting fluid in. If nothing
happens remove plug and ground it with the wire attached. If you get
spark backfiring indicates a timing problem and a sheared flywheel key.
If no spark you have to trace it back but start with a new plug. You
need 3 things to run air, fuel and spark. No spark is plug, plug wire,
coil -points-condensor, or coil ignition module. Or broken wire or
stator. Backfire is timing , flywheel key. Maybe no compression also.