When the rider turns a key to switch on her motorcycle’s ignition, this action applies power to the ignition module, an electronic device used in the creation of spark. Then she pushes the starter button, which activates the starter motor. If there is no starter motor, then the motorcycle will be started with a kick-starter rather than a starter button. The starter motor or kick-starter rotates the crankshaft and the engine starts.

The crankshaft is connected to each piston by way of a rod (one rod per piston). Each piston is located in a cylinder. These pistons push in and out of the cylinder to create the four strokes of a four-stroke cycle; the camshaft, which is connected to the crankshaft, opens and closes the valves. Each full turn of the crankshaft produces two strokes of the cycle.

What the Engine Does After Motorcycle Ignition

Generally speaking, these are the four actions that make up a four-stroke engine cycle:

Intake stroke: The intake valve opens; the piston goes down, creating a vacuum that sucks in air and fuel. The intake valve closes.

Compression stroke: The piston pushes up, compressing the fuel and air mixture. The crankshaft position sensor detects that the piston is approaching top dead center, and tells the motorcycle ignition module that the coil should spark. The insulated spark plug is connected to the coil, and carries the spark into the cylinder without actually leaving a hole – hence its name, plug.

The method used to trigger the ignition module varies between motorcycle models. The correct time for a spark, which is an electrical arc somewhat like a bolt of lightning, is usually a few degrees before top dead center. As the engine speeds up, the spark is usually advanced, which means it occurs sooner – even more degrees before top dead center.

Power stroke: The piston descends, letting the ignited gases expand. This action is what would power the motorcycle forward if it were actually in gear, and keeps it running if it’s in neutral.

Exhaust stroke: The exhaust valve opens. The piston goes up and pushes out the exhaust. The exhaust valve closes.

Additional Notes About Motorcycle Ignition

Because the piston reaches top dead center twice per cycle, in many motorcycles the spark will fire twice, even though on the exhaust stroke there is no fuel for it to ignite. If some of the fuel has not been burned, there can be a backfire through the exhaust.

Older motorcycles may not have an ignition module. They may have points, or mechanical switches. The points connect directly to the coil and are opened and closed by a lobe on the camshaft or crankshaft.

The advantage of ignition modules is that they have no actively moving parts; points must be maintained, and eventually replaced.