New 09. Bought it 2 weeks ago. Finally had time to ride it Saturday afternoon, after the dealer was closed, so I couldn't call the dealer and ask. The dealer removed the AIS, uncorked and rejetted it for me. I told them to jet it for a QCore. When the engine is fully warmed up, the stumble happens at 23mph in 3rd gear. I'm guessing that the engine is turning around 3500 RPM. Every bike has it's ideosyncracies. This one is new to me. So I just don't know how smooth that engine is. It pulls hard and I'm very pleased with the power this thing makes. Other than the stumble, I'm very pleased with the WR 250. While I'm on the subjet, If I put a plate on this bike, and ride it on the road, if it's jetted properly, how smooth will this thing cruise at a steady rpm?