High RPM Issue on Dyno

Someone spit in the carb when you weren't looking ! In high school auto shop, Mr. Kingham would have the sun - scope all hooked up to a running car and while he's looking at the scope - all of a sudden the thing would go biz erk ! He'd put his hand on his head and scratch - the second time hit the side of the machine - LOL ! The good old days :D