My son raced a decked out TTR125 for a while and we made th switch to the KX 100 last winter. There is no comparison. As modified it is an exceptional trail/HS/Enduro bike with significant low end. We did and learned the following:
1) ST pipe and turbine core muffler
2) Boyeson Pro Series dual stage reeds worked well, however, the bike runs much quicker with carbon tech low tension reeds
3) Jetting - dropped 2 main jet sizes (I think we are running a 132 main now - still blows spooge but runs very crisp)
4) 32:1 synthetic 2-stroke oil (we are running Motul) with VP C-12 (I know all the arguments about the pros and cons of race gas, compression, etc. - but it simply runs cleaner with the VP)
5) Triple clamp, fat bars and brush guards
6) Twin Air air filter with NoToil
7) 428 chain conversion with an extra tooth on the rear - we add an extra tooth on the fronth for desert riding
8) Full skid plate (not the little MX glide plate)
9) IMS fuel tank
10) Excel rims - these were replacements for the stock rims that got square in the rocks
11) Michelin tires
We change the oil after every 2 rides, clean the air filter after every ride and the bike is very reliable. BTW, with these mods there is no need for a flywheel weight.
I'll post a photo if you want...
Have fun!