Check your cylinder through the exhaust port to make sure that it is clean an no scoring on the cylinder/Piston. Also try to start with the muffler off but make sure you have ear muffs on.
If you are in the country area check for a wasp nest in the muffler as this will cause the same symptons that you have.
Regards,
Bruce
Please do not PM me asking for support. Post on the forums as it helps all members not just the individual.