you don't have to take off the tank- look on the right side through the trellis frame and you can move the throttle by hand. I haven't seen one with a major vacuum leak, but I'd check that as a secondary measure. and a jammed piston? someon'e talking out their ass. Jammed piston is major internal engine damage and it won't run. with a desmo you'd have to skip the belt or suck in an airbox full of water to accomplish this kind of damage.