Slipping kickstart

What have you done so far, did you change layshaft 1st first gear or check the fit on the layshaft.

Happened to me on my  99 and on a mates 650SS ,  on both occasions I found the pawl had been fitted upside down.  Worked for years like that !,  If not you are likely to need a new pawl and possibly  the gear.   Job took me 30 mins  in the IOM ,  Still find bits of grass in the oil.  

This happened to me with my 750 Commando rebuild.

I replaced the pawl etc & it was no better.  It did sound & feel like the pawl was slipping - except it wasn't !

I got a friend to observe the prinary drive, whilst I operated the kick start.  It turned out that the primary chain was jumping off the sprocket.  Close examination of the chain revealed several cracks in the side plates.  All at different points, so the chain appeared to be ok unless you looked really carefully.

A new chain cure it.

Hope this helps.

If you changed the pawl to a new one and checked the layshaft first gear bush is a sliding fit on the layshaft then next step is new first gear. If the bush has excessive clearance then the first gear can move enough so the pawl slips even if new. The bush can be bought separately from the gear but you may consider another strip down of the gearbox too much bother and just go for a new gear which should come with bush installed.