You can discover the mixture of your fuel by the simple evaporation method.

Measure out a specific amount of your fuel in a graduated cylinder. 100ml is a good amount, but not necessary although you must record the amount in the cylinder.

Now place the cylinder where the fuel can evaporate, but no foreign matter can enter.

Once the ether evaporates off, the oil & kero will separate - giving you the two major fuel components, and the full mixture by calculation.

Your sputtering run - if the fuel was close to described - could be due to being undercompressed, or lean/rich.

Keep on mate.