Vinnie and the Vacuum
RAY: The resulting effect wasn't bad for the car, but for the vacuum it was very, very bad. What happened to Vinnie was that his vac was blown to pieces. What had happened was that on one particular cylinder, the intake valve was in the open position. When he held the vac's suction hose on the spark plug hole of that cylinder, he had unwittingly sucked in a gas-and-air mixture into the cylinder from the carburetor, just as a descending piston would. Except in this case, it went up the vacuum hose and through the catchbag, only to be ignited by the electrical current at the motor's electrode. This sent Vinnie's trusty Electrolux into many airborne pieces. Fortunately, they all missed Vinnie.
[ Car Talk Puzzler ]