Many years ago i noticed many of my .049's ran much better on cox fuel than they did on other brands with comparable percents. This prompted me to call cox and talk to them about it. That led to many phone calls to fuel suppliers and somewhere along the way i talked to someone who said they used to mix fuel for cox, and i was correct in that there was a extra ingredient in cox fuel that others didnt have. He said it was ether an ignition improver, or a combustion enhancer, i dont remember which. Could it be amyl nitrate, the same stuff in diesel fuel?

Definitely NOT Amyl Nitrate. My best guess is Propylene Oxide.

It could be! I used to race karts and one of my competitors cheeted and used that in his fuel.

Amyl nitrate is for diesel fuels, AFAIK it doesn't do any good in a glow fuel.

Hey tim, what does AFAIK mean? I here that alot.

I too hate acronyms.  The phone used a lot of them and we spent a lot of time trying to figure out what the educated people were trying to tell us. 

Getting back to the original question, Cox fuel formulae have been published repeatedly if you do a search.  However, in the Christmas Holiday spirit, here they are again:

Sport Fuel  15% Nitro 18% Castor Oil, (2% Lubricin in the Gallon Cans) and the rest Methanol

Racing Fuel 25% or 30% (depending on management's mood) Nitro, 18% Castor and the remainder Methanol.

I currently run 15% Nitro, 10% Castor, 10% Synthetic for Cox engines and 10,10,10 or 10,11,11 for everything else.

Since I fly competition aerobatics, I need total reliability, not expecially great power so the extra Nitro isn't needed.  One of the guys is using an AP Wasp with a drilled venturi, pressure fuel system and 25% Nitro.  It works for him!  230 sq.in. plane on 50' lines and completely reliable performance. (Current holder of the Leprechaun "Pot 'o Gold" Trophy)

   Many years ago i noticed many of my .049's ran much better on cox fuel than they did on other brands with comparable percents. This prompted me to call cox and talk to them about it. That led to many phone calls to fuel suppliers and somewhere along the way i talked to someone who said they used to mix fuel for cox, and i was correct in that there was a extra ingredient in cox fuel that others didnt have. He said it was ether an ignition improver, or a combustion enhancer, i dont remember which. Could it be amyl nitrate, the same stuff in diesel fuel?

Hmmm, I have no problem with normal 15-25% nitro fuels (like Sig) in my Cox engines. As long as I have 1) a good igniter, 2) everything is sealed up ok (like tank backs), 3) the reed isn't glued onto the holder by old castor, 4) the needle is not loose and leaky (piece of fuel tubing usually fixes this),  the engine will start and run every time. No extra bug juice is needed.

Sounds like the "Secret Sauce" as in Kung Fu Panda!