Need jetting tips

The LTR jetting kit was developed specifically for the GasGas EC/XC 200/250/300 models which use Kehin carburetors. It is not applicable to your YZ125 which uses a Mikuni carburetor.

If you search the forums, specifically the Japanese bike forum, I'm sure you will find a ton of topics related to jetting for a YZ125. Unfortunately, no matter how sharp you get the jetting it won't make a substantial difference in low-end power. MX 125's make the majority of their power at high RPM's and therefore need to be ridden hard not "lugged" through the woods.

Both Trailrider and Dirt Rider (or was it Dirt Bike) magazines published articles on setting up a YZ125 for off-road (enduro/hare scramble) use. If you can find those articles, particularly the Trailrider article, that would give you a good starting point.