I have had two KX 100s, both big wheel models. The first was a 95 which is a non power valve motor. It was used and ran thru both my kids for 10 yrs or so before I noticed it was down on power. Never fouled a plug or broke down. I put new top end in it and it ran great again. This model is the 95-97. If I remember right they went to a PV motor in 98. I now have a like new 02. It is the PV model. It has a FWW, I had the cyl shaved to lower port timing to bring power delivery down lower in the rpm range. The older one got hard to find after market parts for, the new one I found everything I wanted-Kick stand, skid plate, alum spark arrestor, FWW, and a big tank is made but I have not spent the dollars for that. The newer PV motor does have two problems I found while looking thru the net- the cranks go out if you run them too lean on the jetting and the PV is a booger to work on if you take the timer part of it apart causing it to break.
Both are great 2nd bikes, have super top end power, but will pull and lug in the mid all day and not foul a plug. Lite, easy to start, short, etc. Get one and you wont be sorry.