I had a speed up kit put onto each of my walkers. Both 20HP. One has 42" the other 48" deck. There is a HUGE differance in speeds, the 48" didn't speed up at all. I don't htink it's the decks weight though. The slower mower did get jerky, and the fwd control is much tighter to push/pull now. I took it back and the shop said it was fine. They said it could be an RPM issue which didn't make sense in this case. They had just tuned it up, plus it runs great when not in motion. They just didn't want to make time for this that's all. Any ideas on why this would happen? There is no other dealer within reasonable distance. Thanks for any help.