I need a light weight bike with a recluse clucth, low gearing, preferably KTM,  The need is for a bike for access washed out roads. Top speed needed is 45 mph, expect to be riding and or pushing the bike while powering it through very difficult terrain. It is not for motocross or even pleasure trail riding, the use will be very utilitarian. Where do we start?
Currently I own KTM, sx 85(kids bike), xcw 400, 690 enduro R, and 990 superduke.  Light weight and able to drive thourgh the roughest conditions is the sole purpose of this bike.

Would this set up work well on a 144 or 200 smoker KTM?  or would you sudjest a heavier 4 stroke?