My first engine was a Fox .40 BB deluxe (with the air-bleed EZ-carb). I followed the instructions that came with it and had fine performance and reliability from the start. Many gallons have been though it and it is as good as new. This is with 0-5% nitro fuel, which is relatively inexpensive. It was less expensive than a comparable OS engine, is a true ABC engine, and is very light.

Fox engines have a reputation of being "difficult" and the "experts" at my club (where the 2-stroke engines are most commonly OS's) generally said that it was a poor choice for an engine. But I don't think that there is a better running engine at the field, from idle to wot. I have a Fox Eagle 4 .60 engine and it too performs really well and is reliable (again, I carefully follow the instructions that came with it).