I just got back from riding at pismo beach. While I was there I noticed that my dad's 06 yz250 had a weird surging idle, then about 7-10 seconds later idles normal. It started about 7 minutes after riding hard, lots of wot and jamming from gear to gear. It only does this after the bike is warm and lots of wot and then stopping. I think it may be detonation as it sounds like knocking. I didn't notice any pinging while riding under load at low throttle opening, just surging at idle. I turned the air screw out half a turn to see if it would help and didn't notice a difference. It has been jetted for 40:1, pro cicuit pipe and silencer running 91 octane fuel. I may try some av gas but not sure if it is safe for the bike?