2 The crank drive pulley could be increased in size ,possibly adapt an alternator pulley or decrease the size of the pulley on the gearbox but in doing this the V belt will most likely need changing to a more appropriate size. (little bit of a hassle though)
3 The wheel diameter of the back wheels can be increased by using liquid nails to glue a larger tread rubber to the outside of the existing wheels the front wheels would need to be swapped for larger wheels to even out the mower ground height. ( just don't have the mower so high that the blades are too high when the Height adjustment is on the lowest setting)
4 Depending on what rear wheels the mower has at the moment you may be able to fit larger standard Honda wheels as I have a couple of self propelled Honda mowers and the wheels on both mowers are different diameters.
5 Replace the 3 speed gearbox .
6 Make sure the drive belt isn't excessively stretched or worn and slipping all the time.
