Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Welcome to JUST ANSWER small engines, let me try to help you !! I don't know it all, but maybe together we can get you a satisfactory answer!
Check the linkage at the transmission, the lever may not be moving as far in reverse as in forward. The length of the throw is what determines the speed. It moves the inner swash plate, which moves the inner pistons for more speed. The reverse is not moving far enough. # 163 in the link below shows the control rod. Be sure the reverse pedal has not slipped on the pedal bracket.
Did you find why the reverse pedal does not move far enough?