The Varo Amp-Champ was powered by an Ohlsson & Rice 2-cycle, single-cylinder model airplane engine (Type 122) that was rated at 3/4 HP at 6,300 RPM. It ran on 70-80 octane pump gas mixed with oil at a 24:1 ratio. Joe Martin donated this engine, which was used in the field for starting model airplanes in place of a battery. We are also told that they were used during WWII and the Korean War as portable auxiliary power generators to run field radios for communication on the battlefield. Lighter than a large 12 Volt battery, they would also produce power as long as you had a source of gasoline for fuel.
This is a good example of turning lemons into lemonade when the wartime market reduces demand for a hobby product like a model airplane engine. In typical government fashion, complete instructions for starting and running are printed on a decal on the engine so any soldier could get it running. Plug gap, points gap and magneto gap were all right there as were mixture and starting procedures. Although O&R engines were no doubt chosen for their famous reliability, it was noted in the instructions, “Clean cylinder exhaust ports when engine loses power.” Read more about Irv Ohlsson.