That is the only real frustrating part, there are no instructions for adjustment... I just sort of eyeballed it, and it worked great in forward. Since the throttle is fully mechanical on the 2610's adjustment is easy. I adjusted the cable so that the lift arm gets maximum travel. Then I adjusted the nut on the black throttle mechanism so that the full range of the pedal lever moves the throttle mechanism. It's kind of confusing in text, and the directions stunk, so I made this quick drawing. Hopefully it makes more sense. I made up the terminology... haha.
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Long story short: Since the reverse pedal has a much shorter throw than the forward pedal, it cannot move the throttle linkage as far as the forward one... Net result is lower rpm's (and speed) in reverse. I haven't played with adjusting the stop screws on the pedals themselves (underside of the deck), I don't know if you can adjust the reverse pedal screw enough to increase the linked RPM's.
Sorry for the novel, hope this helps!