Be careful around small engines

So, I washed the 18G today. That's the Gravely angle. While finishing it up, my neighbor comes over to ask if I can look at the motor on the little 1-cyl "toy" quad bike that he got second-hand, non-running, for his kids. I said sure. Electric start only so I put the battery on the charger and checked things over, familiarized myself with the plumbing and electrical. It had a hydraulic hand brake. Installed the battery, checked the key and it wouldn't turn over; found out you need the hand brake applied. Turned over fine; wouldn't start with fresh gas so checked for spark, spark was good. Pulled the carb and blew out all the passages, and fixed a sticky float valve. Reinstalled carb and it fired right up. And took off, ran into the neighbor's garage and was finally stopped by the bumper on his truck. Smashed the cowling on the front of the quad and broke the filler neck off the gas tank. Best I can figure is the brake caliper was frozen and the throttle was on "bunny." Thank god no one was in the path of it when it took off. Moral of the story is respect the equipment you are working on, and think twice before trying to start a machine that you are unfamiliar with. I also think the guy should think twice before putting one of his kids on it.