Castor oil
Four stroke model engines, since they are generally designed to be simple power plants while still incorporating the usual camshaft, rocker arms and poppet valves of larger sized four stroke engines, are generally meant to use glow ignition and their fuel. Often, the oil percentage for four stroke glow fuel can be lowered from the 18–20% figure used for some two-stroke engines, down to as low as a 12–15% (neither YS or Saito recommend using so called 4-stroke fuels as they feel the fuel does not contain enough oil to lubricate properly), but use of such low-lubricant fuel can also mandate the need for a small amount of castor oil in the mix (most modern Glow Fuels contain some percentage of Castor oil along with a higher percentage of synthetic oil), and mandates setting the high-speed fuel mixture carefully by using a handheld tachometer to check engine speed to avoid over-leaning of the fuel mixture.