How do you eliminate the waste spark in a single cylinder engine?

You can't eliminate the waste spark in a true single-cylinder, four-stroke engine using conventional ignition systems. The term "waste spark" refers to the ignition of the air/fuel mixture on the exhaust stroke. This is inherent to the design of simple single-cylinder ignition systems. These systems fire a spark plug every revolution regardless of whether it's the compression or exhaust stroke, because using a single coil and a distributorless ignition system necessitates simpler timing, requiring only one trigger per rotation. The energy released during the exhaust stroke is wasted.

To avoid the waste spark, you'd need to change the fundamental ignition system design. Here's how:

* Individual Coil per Cylinder: This is the most common approach for multi-cylinder engines, and is also feasible for single-cylinders. Each cylinder would have its own coil, allowing precise control over when a spark is fired. The engine management system (ECU) would only fire the coil during the appropriate compression stroke. This is more complex and expensive.

* Lost Spark (but not exactly "waste"): While not technically eliminating the "waste" spark, a lost spark system uses the same coil but intelligently drops the ignition pulse during the exhaust stroke. This still uses a single coil, but is a more sophisticated approach than the simple waste spark, using sensor feedback to control which pulses are truly fired. Essentially, the "waste" spark simply doesn't occur.

In summary, there's no way to eliminate the *inherent* waste spark of a simple single-cylinder, single-coil ignition system. The solutions involve more sophisticated and expensive ignition setups, essentially upgrading beyond the basic waste spark design.