I have a fresh motor, new topend, starter gear?

Sounds like the starter drive is not engaging. The starter drive on the starter is not engaging into the flywheel. You would be able to hear the motor on the starter it is just that the drive gear on the end of the starter is not coming out to the flywheel .

Engine is under max load in the situations you describe, so any weakness in spark or low fuel prssure can cause this, even a weak ignition module.

clean the carb jets etc and check fuel pump diaphrams not hard or perished ! balance the carbs also !

Who put the new crankcase seals in your bike? Sounds like your sucking oil out of your crankcase if it is blowing all that smoke.just fixed Cr125 doing same thing.

I’m happy to assist further over the phone at https://www.6ya.com/expert/michael_18b4936ebf017b21

The left blade on a BD 2300 bread maker did not turn when neading the dough. I took it apart by removing the six screws in the bottom of the case and the screws inside around the bottom outer edges of the metal insert. I then removed the screws holding the motor assembly to the base. I found that the metal plate attached to the paddle shaft driven by the gear had torn through the plastic gear, and was no longer driving the paddle. I made a new plate with the end bent down 90 degrees so that it fitted into a slot in the plastic gear. This is much stronger and the breadmaker now works fine. This is a weakness in the design and the failure could occur on either paddle. failures of the left paddle could be due to the toothed belt breaking, this drives from the right paddle gear. There is also a belt between the motor and the left paddle gear.

its usually located on the the bottom side of the engine next to the flywheel . if you got the right tools it shoulnt be that hard to replace

hi m8,, first try this, take the handle bar start button switch gear appart,,and clean the starter button terminals that connect wen u push button in,,spray some wd40 inside the switch gear wen u put it back together,,,,,often after off roading ,,connections that the eye cant see corrode wen the bike is washed down,, any probs still ,, shout and il anserw m8,,,,,cheers

no you **** going bigger in the back is more accel, smaller is more top end. a 48-46 would put you somewhere between 80-100 mph depending on the engine but result is **** low end. If your kx is 6 spd you would benefit from going up a tooth or 2 for lowend because it has topend already.

i hate to tell you but i think you have a weak starter what happens is the windings in the starter short giving the starter less torque.