Small Engine Troubleshooting Problems? Ask a Mechanic Now.
If you remove the spark plug ,and with it grounded, do you have spark?
If it has spark, do a compression test. put finger with rag over spark plug ole and see if it has enough compression to move your finger.
2 cycle engine or 4 cycle engine?
The four cycle can have valves too tight, causing backfire. Two cycle has no valves! To check spark plug you remove it, lay it on the metal of the engine, so it is grounded, and crank engine and watch for spark at the plug tip.