So Ive been having this problem with my 2011 YZ250 that it starts bogging at the top end and then eventually stalls. The first time it happened the bike was running fine for the first hour and then it started bogging when revved and then just died. So I changed the plugs with a new one and it kicked over but then still had no top end (might not of screwed the plug in far enough?) and my mate noticed fuel coming out of the pipe. After this happened I took the bike to the store and they re-jetted the bike to run a little leaner, clean the carby and repack the exhaust (I get splooge dripping from the exhaust seal onto the rear swing arm). Before this I was running 40:1 using Motul 800 oil. After getting the bike back the store drained the petrol out of the tank and advised to use Silkolene KR2 oil instead with the ratio of 32:1. We went riding on sunday and after around 1-2hours of riding (mostly lugging around on a enduro track) I gave the throttle 2 big blips with the clutch pull in on 2-3rd gear and it started bogging again at the top and then eventually stalled. This time I changed the plugs again for a new one but the bike wouldnt kick over at all. I took it back to the car and my mate managed to roll start the bike and he said it sounded fine. The bike has plenty of compression and will normally kick over 1st go with no problems. I think the bike might be flooding and it could be how I'm riding the thing. The spark plugs look fine and are not fouling. Any ideas?