Hey, my buddy is about to buy a 250x thats really clean for round $500 but it has somethin wrong w/ the carb, it seems that it won't run unless you hold the choke lever in a certain place. Its a 400ex carb and the kid said he had already had problems w/ the choke but he had it fixed but now its doin somethin totally different. Any thoughts as to what this could be? Thx.