Canabian, what are you using for fuel now?

Model diesels run on a mixture of kerosene, castor oil, ether, and an ignition improver such as amyl nitrate. Kerosene is for power, castor oil is for lube and cooling, ether lowers the compression ratio needed for combustion, and the 2%-3% amyl nitrate makes it all work better together.

Some have used substitutions. Most go back to the standard mix.

Gunk? What will that do except keep it clean?

I would suggest you purchase a can of ready-made diesel fuel and leave the experiments until the engines are broken-in and you are familiar with diesel starting and operation.

You may find the longer stroke engines such as the Mills replicas more tolerant of other fuels.

Good luck,
George