OK so the last thing to repair on my Wr450 would be its nasty habit to STALL when it idles. So here's how it goes

ride for a bit engine works great, tonnes of power in every gear very smooth through the rpm range, close the throttle and come to a stop and let the bike idle, very quickly it will stall [about a minute]. When I go to kick it over it usually backfires once then starts up perfectly, will idle for a while and stall, I have to rev it a bit to keep it going. its not that it is idling too low, I have it up at a pretty good rate. Any idea why this is happening? fuel air mix wrong? maybe due to the uncorking i need to re-jet the bike? Just stop being lazy and clean the damn carb?