Abstract: The invention comprises a spark booster for use in the ignition system of an internal combustion engine. Two embodiments of the invention are disclosed. Each embodiment comprises two electrically conductive members which are spaced from each other to define a spark gap, a bi-metal disk for varying the size of the gap in response to variations in engine temperature, manual adjustment for adjusting the spark gap independently of temperature, and an inspection window for visually observing the spark gap. In addition to the foregoing features, one embodiment also includes apparatus for varying the size of the gap in response to the load on the engine and its speed.