Thanks for contacting FixYa. Fixya is going through a software upgrade so you will get a lot of responses to your issue. We all have the same goal in common -
to help you the valued customer. I'll lay out a strategy that will get your
power problem resolved. Other techs may comment to advance the solution.
http://www.bikez.com/motorcycles/yamaha_xt_125_r_2006.phpFree Service Manual:http://bmanual.com/Yamaha-TTR125-2006-Service-Manual.htmlRoot Problem:Your bike is running too rich from over fueling! Won't build torque or rpm.
Steps:- Clean your air cleaner and spray it with light filter oil.
- Check your exhaust pipe make sure it's not plugged or restricted
- Gear ratio - too many teeth on primary sprocket?
- Install a new or clean spark plug for color testing. Want a cocoa brown.
- Jetting - Needle Valve - Raise the cir-clip a notch at a time lowering the needle into the pilot jet. Mostly effects the mid-range 35 - 60 mph.
- Jetting - Main Jet (should be OK) if it has been changed/increased to a larger orifice you may want to go back to stock. This usually effects speeds when the wire is tight and your running is WFO. Wound Flat Out.
Worse case scenario:If this bike has a lot of hours on it you may want to freshen up the top end. Re-ringing the piston and honing the cylinder head with a good cross hatch pattern works wonders to get power back. We used to do this every couple of races. If the cylinder is slightly oval shaped it needs a bore and next over piston and rings. (Most frequently a problem with 2 strokes) Hope this helps and keep us in the loop. TF
