In reference to my post further down about the 426 stumling on throttle, seems to have power no power on throttle but idles ok, I am going to check out the carby, timing settings and electrical resistance. I do not have the owners manual but have one for the YZ450FR, are there any difference in the electrical system between the two or are they the same? If not does someone have the resistance Ohm specs for the coils etc for these bikes (YZ426F 2000 model) that they can post for me or email me the specs at email@example.com The run down on what is going on is the bike will start and idle, initially seemed ok, took for a test run, accelerated up the road ok after about 300metres started to lose power on twisting the throttle and would surge on and of, plenty of power when it did come on though. Backfiring on decel and spitting blue flame out of exhaust. I have just got the bike cheap. It is possible that the tank was filled with unleaded instead of unleaded premium, is this an issue? Could water contamination of fuel cause this problem? The only thing I have really done is replace the chain and sprockets and the front sprocket was a real pain to get of, I believe the service dealer must have used a rattle gun to do it up without torque specs, was way more than 54lbf. Any suggestions would be appreciated.