Same bike as the Quest 650EX. I found this video on youtube and my bike is doing the exact same thing. The person that shot the video said it was a bad rod bearing but I am not convinced. My bike has been at the shop now for 2 weks and they rebuilt the carberator but the bike will still not start. Without taking the motor out of the bike they seem to think it is something internal but are not sure what. Anyone have a similiar problem or solution? http://www.youtube.com/watch?v=I6OqvPnuE1A