Up untill 1947 all model engines were spark ignition and ran on a gasoline oil mix. Most ranged fron .19 to .60.The problem with these engines for most current day uses is that they have manual spark advance, and aren't easily throttled. They were/are used primarily in control line and free flight model aircraft and in tether cars.

Fox is now producing a throttled spark ignition .50, though I have never seen one.

jess