It could be dirt..
Remove speeder 'tab' from top of the carburetor , and blow
high pressure air down- inside the carburetor. If possible -
then try to remove the fuel hose too, and blow air.. to REMOVE DIRT from carburetor.
Or, if oil hose is leaking (just a little), the oil runs directly down
into the air filter. WASH FILTER with easy chemicals .
Cheers ,
Christian, May 2008