I just thought of another possible problem you may have a slipping manual clutch. Because when I installed the centrifugal clutch the manual clutch loosened up so I Had to take it all apart to fix it
Ok now how to get it apart.
Carefully pry on the centrifugal clutch outer housing all the way around. It will loosen up and you will be able to pull the clutch weights and the outer
housing off the motor. Then you can get at the screws for the clutch cover.
With the cover off put the outer clutch housing back in and spin it by hand to see if the manual clutch spins. Make sure the manual clutch is engaged with the rear wheel locked in place if the clutch gear moves the manual clutch needs to be tightened up If the manual clutch is not slipping then you will know that the centrifugal clutch bad.
Hopfully this will be you when you done