I bought an 87 250x about a week or so ago had some problems with it. Just recently fixed the decompression lever and rebuilt the carb. Was having trouble with it idling but now seems like it will sit and idle all day. Seems to run good and strong until it gets warm then shuts off and is hard to start again. Any help would be greatly appreciated been wrenching on this thing since I got it and I just want to ride. The one I had in high school I ran the heck out of and never had to do anything to it but this ones been a headache.

 

Made sure the tank vent is open along with any carb atmospheric vent? This can cause a vapor lock on getting fuel to the carb if you don't and may take time for the carb bowl to refill.Plus have you checked the valve clearance along with a compression check? This could be part of it or even the ignition could be breaking down when warm. I'd find a good manual for this model and go through the trouble shooting guides and resistance checks. Plus when it quits,pull the plug cap, have a fresh plug handy and check to see if it has decent spark.