I have a Countax C800 with a 42" deck, which doesn't cut as well at snail's pace as my old Mountfied Mirage does at walking pace. My thoughts are that the pulley size is wrong and therefore the blade speed is too low. Countax say there isn't a design problem, and haven't rectified the problem.
any ideas?
Interfering with the pulley size will affect the length of the drive belt you are using, so I wouldn't go down that route.....make sure that both blades are sharp and the deck is set right - 28mm at the front, 36mm at the back.