Welcome to the forum Gully!
It sounds as if your friction disk is out of adjustment. It is the vertical rubber edged wheel that contacts the metal drive disk when you depress the drive handle. Look at the bottom of your machine and move the gearshift from speed to speed. Notice that all of the forward gears put the friction wheel over the same half of the metal drive disk and if you select a reverse gear the friction wheel is positioned on the opposite side of the drive disk. Adjust so that all the reverse speeds are on the same side and all the forward speeds are on the opposite side.
Marc
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