Terry,
Can you have a look at a couple of things?
1. Remove the muffler and see if you have any markings (scoring) on either the piston or cylinder.
2. Check that you have spark at the plug.
3. Check the fuel filter in the tank to see if it shows signs of dirt.
4. Never use Aerostart on a two stroke mower as it does not have any lubricant and will damage the engine.
Answer these few questions and I should be able to give you some answers.
Regards,
Bruce