GMC--- Here is the way it works.
Starting with the #1 piston at TDC compression stroke. The spark plug has just fired and the fuel in the cylender burned, piston go's down, exhaust valve opens and piston starts back up pushing the burned fuel out of the valve, the piston nears TDC again and the intake valve opens, the piston go's down and sucks in freash fuel, it reaches bottom and the intake valve closes, now with both valves closed the piston compresses (compression stroke) the freash fuel and when nearing TDC the spark plug fires and starts the process all over again.
It is critical that you are on the compression stroke to properly position the wires on the cap.
