my 06 crf450x fires right up (choke on, tap the start button), but if i don't let it warm up past 140ish degrees before trying to take off, it'll stall if i don't feather the clutch more than usual. if it stalls, i have to either choke it or just hit the button 2 or 3 time to get it to crank back up quickly. it doesn't do it every time, just sometimes. it just recently started doing this since the battery drained a couple weeks ago, and i don't know if that has anything to do with it. i've never had a problem with the valvetrain at all, but at first, i was thinking valves need to be checked, but since it fires up with ease, they might still be in spec? they were checked/shimmed about 30-40 hours ago. when they were out of spec last time (after about 100-150 hours, the bike still started and ran fine, but i had them checked just cause i wanted to. i run premium pump gas, and the bike was also jetted correctly last spring/summer for the MRD exhaust. any ideas on what could be causing this?