See: https://www.cyclepedia.com/yamaha-xt250-troubleshooting/
We were nearly complete reassembling our 2009 Yamaha XT250. The bike as delivered to us never quite ran right and the seller was anxious to get rid of it — he said he had cleaned the carb and gone through everything. When we got the bike it would run okay for a few minutes. Once warmed up, the engine start to stumble and bog under anything more than 1/4 throttle. It was cutting out so bad it sounded like it had a rev limiter at 3,000 rpm. However, all of the electrical tests checked out fine. The machine had very low miles and looked brand new. There were no indications of a mechanical problem. CYCLEPEDIA’s experienced technician was confident it was a rich running condition that was causing the problem…. Read more at: See: https://www.cyclepedia.com/yamaha-xt250-troubleshooting/
Post time: Aug-07-2017