Why wont my 2003 kx125 hit the power band, right as it would hit it it just back fires

firstly its always better to change both of the bands even if one is broken this always keeps the drive trim.all seems well clean all the contacts ie battery and gun (do not use any cleaning products this will cause grease)just wipe clean with paper towel.

could be a jettng problem or a sign your rings are starting to wear out. have you noticed any loss in power? try running a compression test.

Be sure the exhaust pipe is not partially plugged up with dirt. If not, remove the exhaust pipe and go for a quick ride down the street. If the power band is back, the pipe has an internal blockage. If not, then remove the carb and air filter for cleaning. If no luck then pull the head and run the piston to the bottom. Check the exhaust port for carbon build up. Clean out any build up with a screw driver, preferably from the exhaust side. Decarbon the head and the top of the piston and reassemble top end and exhaust pipe. If still no joy, the crank seals, (and possibly the crank bearings) probably need to be replaced.

its prob your magnito with out a good connection to magnito it wont spark at all,could also be spark plug wire



My bike,
Kx125

i have a 92 rm 250 an i just had it fully rebuilt an it laggs in power band an splutters an feels guttles

on carb is a screw buddy fiddle with tis screw till it runs i had this problem as well

Sounds like it's trying to sieze if it's fluctuating and won't wind up. You may have to pull your cyledar back off and mike it to see if it is out of round and within specs.

Your barrel? LOL. Sounds like the valves need to be gone through. I would suggest taking and valve train apart and put it back together correctly then go from there.

Cylinders are from left to right as standing in front of the car. Number 1 is the first plug on your left & 4 is on the right. The coil pack is numbered. Simply connect the wires to the right plugs.