Engine seized? i was changing up a gear when my yz250f made a whirring sound and cut out. Tried to kick it over and kicked a couple of times then the kick start seized, any ideas what this could be?

If you can bang the transmission into neutral and she rolls - the bottom end is seized up. If you can't get the transmission to go out of gear you have a gearbox problem. Found this on a Kawasaki forum that describes a similar situation to what you're experiencing - https://www.kawasakimotorcycle.org/forum/kawasaki-motocross-offroad/41961-kx65-engine-locked-up-im-going.html

sounds like the kick gears are worn ! remove side case and check condition !

the way you are describing it the engine is seized
but if the engine will turn over on the flywheel bolt
then it could be a couple of things
using your kick start (if your kick start does not move when pressure is applied then your engine is seized)
(remedy) total engine strip
("your kick start just goes up and down not doing anything")
seized clutch
remedy strip your clutch and clean up
("if a clicking noise is heard when using the electric start but your engine does not move it is your starter solenoid")
take off old one and replace and replace

Your clutch basket is the link between the engine and transmission. Your kick starter rotates the clutch basket gear, which turns another gear at the engine crank. Remove either the basket or gear at the crank and see if the engine, and the transmission both turn. Sounds like the engine is stuck for some reason. At least you can cut the issue in half.

Remove the spark plug, put the bike in fourth or fifth gear then try a jump start but with the key turned off. If the rear wheel locks up when you jump on and release the clutch then the piston has probably seized up OR the kick start-to-clutch hub gearing is messed up. The best thing to do is to remove the left engine side cover and look at the kick start mechanism. You may need to remove the clutch assembly for a full inspection. With the clutch removed the rotor ( crankshaft flywheel ) should turn. If it will not turn then a seized piston, broken cam chain or dropped valve is likely. If the rotor does turn then the kick start mechanism is the problem. Please rate my answer. Thanks!

It sounds like it has seized up. Hopefully just the piston rings but you will have to take the engine apart to check.
Good luck.

Hi , Sorry to hear this about your bike but follow these instruction . Firstly remove the spark plug . put your bike with the back wheel off the grown and in any gear try to turn the back wheel . due to no compression you should technically turn the rear wheel in gear . If this does not work and it will not kick start without the spark plug out and still remain seized i am afraid that you will need to look at getting a new top end rebuilt . Give it a try and let me know how you go .

It seems that your clutch plates have worn out. The automatic gears system uses a centrifugal clutch which automatically engages as the engine rpm increases. If the the plates are worn out, it will make a whirring sound as you rev the engine & there will be a loss of power transmitted to the wheels resulting in slow pick up of speed. Get the clutch plate assembly replaced.........sodeep

check the kick stand switch...it sounds like it sticking out....so even when you put the kick stand up the switch is stuck out....so the engine wil cut out as it thinks kick stand is still down....give it a spray with wd40...or something like ....but work it till it no longer sticks.......

Sounds more like a seized engine to me. When a kick starter breaks it will be when you're kicking it. If the engine died and the bike doesn't turn over with a kick it's probably locked up. Try pushing it back and forth in a higher gear and see if the engine turns over when you let out on the clutch,