I just bought a used 07 EX 250 for my wife. I tested the bike in a Von's parking lot and it appears to be in good condition. However, when I rode the bike home at speep of 65 mph and I let both hands go, the handle bars started to shake back and forth violently. It was like a tank slapper. When I put my hand back on then it stop. I'm not sure what is wrong since my first bike was a 600 and I never rode a 250 before. What do you guys think?