MR915 said:All 40 year old transmissions can benefit from undercutting....they could have when they were new. ;D
Will Barber said:All Kawa Zeds can NOT be shifted into 2nd gear unless the output shaft is turning, i.e. the bike is being ridden!
As for it slipping out of gear under load, this is quite common and you more than likely have a bent selector fork. The crankcases will need to be split to replace the fork.
Regards, Will