However some fox engines, like the fox eagle 60 does require a higher nitro content. I belive the instructions say 25%. Do check the things that stick 40 suggested. If it is spitting fuel out the muffler then the HSN is to rich. Start with it only about 1 turn out until it starts. Keep the glow plug heater on unit is has been running for about 30 - 40 sec. Good luck.