recently acquired a gilson brothers tiller , model 51135, and have a problem with the drive wheels not disengaging when putting lever in neutral...tines stop but not drive wheels. Is there an adjustment somewhere to correct this ???? Everything else works as it should ,just can't seem to find neutral in drive wheels......also would like some info on how the 5 speeds operate and settings for it.. A manual would be a big help if anyone had one to copy.....thanks