I take it that the engine is a 2-stroke. Are you using the correct 2-stroke oil in the correct petrol to oil ratio. Should probably be 32:1 but check your handbook. You may even be able to go to 40:1 mix which would make it run cleaner. Try a new spark plug of the correct make and grade too.
ChicksFan
September 2012
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix lawn mowers.