I have an older model...12-15 yrs. Last year the clutch
began to slip above 1/2 throttle...lots of revs but no extra speed.
man showed me the centrifical clutch
ass'y which is a cup on the lower shaft driven by 2 spring loaded brake pads on the motor
side. Apparently oil
leaked from the crank seal over the years accumulating in the cup wetting the pads making them slip.
He cleaned the cup and pads with solvent, all were in good condition including the crank seal. It works fine now.
If you encounter this problem, make sure a hole or two are drilled in the cup perimeter preventing a recurrence.