Hi Jason,

I've heard of folks running these engines on 10%- 15% but these low nitro content fuels haven't workrd well for me or most of the other people I know running these engines . 20%- 30% is the ticket for these engines and equaly important is 20% oil at least some if not all of it CASTOR OIL. I run 30% nitro Heli fuel in my 1/2A cox engines and add 3/4 oz. of castor to a gallon of fuel. If you do try lower nitro content fuels(and I wouldn't) be sure you have no more than one copper shim (head gasket).

Another key to getting these engins to run well is to reset the connecting rod in the piston with a reset tool. I've yet to get a brand new cox engine that didn't need to have this done to achieve peak rpm. The .049 reset tools come up for auction on Ebay occasionaly. You might also check Davis Diesel at http://davisdieseldevelopment.com/ they might still have the reset tool.

Check out the 1/2A forum ther is a Cox engine FAQ that will answer alot of your questions.




Darren