I answered to this question previously, but in spite of putting all this info in the same place will repeat it.
I custom blend my own fuel and after some experimenting found some 'recipes' that work very well for me, probably are fine for other people but not necessary to take as GodSpell.
On mine .12 and .21's use mine own blended fuel by many advantages, the most interesting was the possibility of varying the oil percentage and adapt to different conditions.
Did many tests and those 'recipes' are mine own preferred. Quantities are for a full 1litre of fuel
Summer, temps over 25 - 30ºC.
16% (160cc) Nitro.
6% (60cc) Castor oil.
2% (20cc) Synthetic oil.
76% (760cc) Methanol.
This blend only goes with an 8% of oil (Nova and other mfgs. recomend about a 10% of oil), only for serious racing and 'pushing the envelope a little' (remember: Less oil on your fuel, more percentage of Methanol and Nitro, so more power). Use this fuel only on serious racing, more wear to the engine, but more power. Carb adjustment is vital for the correct opeation and health of your engine - USE WITH CARE!
The same goes for the 25%. For a 30% Nitro, just go 1 point higher on the Synthetic oil (3% total). With the higher content of castor, you're getting a better protection at higher rpms and higher temperature (Castor oil burns at 100ºC higher than Synthetic) but as a tradeoff, more deposits are created on the engine (this isn't bad at all, IMHO).
Practice and 'everyday' recipe. (>25ºC)
16% (160cc) Nitro.
6% (60cc) Castor Oil.
4% (40cc) Synthetic oil.
74% (740cc) Methanol.
The same but for temps from 5 to 25ºC, just change to those values of oil.
7% (70cc) Synthetic oil.
3% (30cc) Castor Oil.
This is a more tolerant recipe, but some brands of fuel use more oil than this (11 to 18% of oil) as much oil you put on your fuel, less power has, but better protection (up to a pont, of course) to your engine, going from 8 to 13% of oil is very common to see.
Of course, other people test can show other results, but those are mine best results with Klotz Benol & Original Techniplate oils. Other mfgs can vary the results.