i have a 08 klx 140l and it don't want to run right it seems like it is choked down and when i take my muffler off and start it up a lot of black carbon shoots out of it and then i put my muffler back on and it runs fine for a about 2 hours and then it wants to quit on me are their any way i can make this better and then it has poor take off it does not want to take off right are their any help for this bike if is please tell me