I need a bit more information on the machine.
1. Check the bottom oil seal to see if you have a leak.
2. John's suggestion could be corret as well with the worn rings.
3. Make sure that the petrol/fuel is fresh as it does go off.
4. Also the condensor could be faulty even if you are getting good spark.
5. Check to see what ring gap you have through the exhaust port by pushing the rings in.
Regards,
Bruce