My kl250 will not start even after valve adjustment

i would say get the stater motor overhauled

Start by checking the start solenoid for proper operation.

Go to you tube, on line adjust valves craftsman 19hp

Your problem is that your valves are not properly adjusted; had the same problem on my 1985 Ninja 600 - the colder the ambient temperature got the harder it was to start. After a valve adjustment it fired right up even in freezing temperatures very reliably.

Sometimes on the Briggs and Kohler engines, the compression release fails to operate at the proper time or is malfunctioning. A remedy for this is to remove the valve cover(s) and adjust the OH valves per the manufacturers specifications. This enables much easier starting, produces less wear and tear on the starter and may allow your new battery to completely turn that engine over. Out of adjustment valves mimic a weak or failing battery quite well and the engine hangs up on the compression stroke because the compression release system is not working properly. Adjust those darn valves.

If your tractor has an engine with overhead valves, the valves may need adjustment. They periodically do on certain engines, because set properly, they enable the compression release feature incorporated into the camshaft to operate. This makes starting the engine easier. Check those valves. If they are far enough out of adjustment, you won't even be able to start the motor.

so if you find your quad his much harder to start after the engine is warm every time then you may very well have tight valves. Which would require a proper valve adjustment. also your valve adjustment should be easy as they are screw and locknut adjusted. hope that helps!

Valves are adjusted by changing the the shims to thicker or thiner ones.
measure all the clearances and write them down, remove the cams and remove the cam buckets of the ones that need adjustment. Note the sizes of the shims removed( it is etched onto them) and replace with different thickness shims to bring them back into tollerence.

Make some marks and notes on the cam timing before removing cams,even take a photo(or that will be your next question) .
valve clearances usually close up( dont get noisy) and valve clearances wont make it smoke, so there may be more maintenance to do, like a cam chain and rings. Im not certain about a yfm, but you posted with a picture of a 2 stroke which doesnt have valves to adjust

If you've tried using a shot of aerostart, and it won't fire there are only two MAIN reasons for that...no spark at the right time, or your valves are not sealing at the right time.

I hope this helps you, as with all problems, I wish I was there to experience what's happening.

Good luck, and thanks for letting us at FixYa.com help