To make a fuel, create a file in the 'config/customFuels' folder with an extension of '.fuel'. Then you have to call for each recipe the fuels.addFuel() function.
With arguments it looks like that:
fuels.addFuel("[input] [duration]");
input is the inputid. It can use damagevalues (i.e 35-2), but only in singleplayer.
duration is how long the item burns.
fuels.addFuel("263 1600");