I now have three of them, a .40, a 2.18 and a .68 that due to weather I haven't got to run yet, the .40 and the 2.18 run absolutely perfect on Fox 5%-50/50 fuel and a H9 Super Plug and I'm willing to bet that the .68 will also, it's in my engine test stand ready to go with a 12.5x6 Graupner on it.