I'm having trouble getting my 98 kx250 to idle right. It runs fine otherwise. Any ideas?

 

I had the same problem with my bike until i screwed in the idle screw all the way in, and after i started it i adjusted it to where it was just right. Also about that rattling sound, i herd it could be the power valve hitting the piston, and i'm not sure if its because i need a new top end. I've herd that sometimes the c clip could pop off, from where the piston connects to the connecting rod, and scrape along side of the piston. I watched a video on youtube of a guy with the same make and year bike as you and it was making the same rattling sound. Have you ever ridden your bike in the sand?

 

Does the rattling your getting hit with every stroke. on my bike its a constant light click on every stroke. I did talk to my boss about the noise and he said that he was pretty sure it was normal as far as he knew. i haven't had the bike in the sand before. also, do run your bike on pump or racing gas?

 

I had the power valve hit the piston on my old bike and trust me you can hear a horrible sound for only a few seconds until you top end is done. If your hearing this al the time theres no way your power valve is hitting your piston.

 

How does your power valve hit your piston?.....unless your powervalve is very dirty from carbon build up...... my 98 doesnt Idle at all unless i blip the throttle.....never has and it runs like a stripped *** ape....crisp throughout the powerband from low to overrev(what little it has) so i guess my question is what do you mean it wont idle?