I have a Grandstand with the same problem. As far as I can tell, the right hand lever, being the operator presence control, has a bit of play in it. If you have the levers in the neutral position and just lightly wiggle the levers back and forth, you will see that the right lever has noticeably more play in it. Thus, when you pull the lever back, it does not make the wheel go as fast.
This is actually a problem not confined to the Grandstand. The commercial walk-behinds with the same control system suffer from the same problem, although it is mitigated by several factors and on the walk-behinds we generally don't use full reverse power so we don't notice it.
It hasn't been problematic enough for me to attempt to find a solution though.
I suppose you could replace the left handle with one just like the right side so they have the same amount of play, but the problem there is that you really would need more travel on the controls to get the full speed range.
The reason it doesn't do it in forward has to do with how the controls are adjusted. If you adjust it so it drives straight forward and its real bad in reverse. if you adjusted it so it went straight in reverse, it would be bad going forward.
Last edited by LCPullman; 09-05-2010 at 02:53 AM.