I am impressed with this setup! It makes me want to lean more towards a shift kit now, would that be logical for my engine? I'm sure I could shim the clutch springs in my ATC70 clone so it grabs at low idle like yours.
http://motorbicycling.com/showthread.php?t=57388
Wild Bill did you ever get your MTB with the jack shaft done YET . It's 2-28-2015 I would like to know how it worked out for you.