Take an airhose coupler and a spark-plug with the porcelin guts removed(be careful, it will make VERY sharp chunks). Solder the airhose coupler to the metal base of the spark-plug.
Set your piston at TDC for the cylinder you want to test. Install the fitting you just made in place of the spark-plug. Hook up the airhose to the fitting and listen for air at the carb(intake valve leak), the oil fill(rings leak)or the tail-pipe(exhaust valve leak).
