Remove the motor assy and you will see the main nylon large gear, it had 2 metal cams under the one screw on top of it. One is the start cam and it must slide freely on top of the other one cam. Over time the grease binds up under the start cam and it doesnt move back in as the motor moves the nylon cogs around and so it start over gain and again. Degrease and lightly lube the metal cam so it moves freely by using your finger, reassemble and test.
Chris
October 2010