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Oil: Castor vrs Synthetic

After using various synthetics with excellent results, we decided to begin test Castor Oil.  Typically with Synthetic, we ran 20:1 for break-in, and 28:1 for racing.  Our motors have lived long lives with at these ratios.

Castor oil seems to need a little lower ratio, 18:1 for break-in, and 24:1 for racing, according to many of the Europeans who have far more experience with Castor Oil then we did.

For those who read their piston/exhaust outlet/spark plug, should note the differences in the decomposition of Castor vrs Synthetics as outlined in Castor Oil 101.  Synthetic simply burns away, where the decomposition fractions of Castor Oil tend to leave a brownish stain of varnish.

The proper color for mixture with Castor is more of a caramel-brown or tan then the "yellowed smokers tooth" color we see on the upper porcelain of the spark plug insulator.  The piston dome should also have a dry tan appearance.  Note the operative word "dry".  Any sheen that could indicate liquid like oil is too rich.  Inside the dome is the best place to look for any dampness.  After pulling the head several times to inspect the color, we decided to use a bent Q-Tip to swab the roof of the combustion chamber for oil.

Castor oil will leave a little more ash everywhere, including the exhaust tip.  The exhaust tip will also have a tan color effect but not as pronounced - it can still be a gray color.

Exhaust Gas Temps (EGT) will not change between Synthetic and Castor.  EGT is not a reliable way to find peak power especially in water cooled motors.  EGT is pretty reliable in warning of damaging temps like a stick if you have a reliable system.   As Castor oil does not tend to burn like synthetic does it consumes little or no oxygen.  Going from 28:1 to 24:1 also means less gasoline is being introduced.  You may need to jet slightly richer with Castor then Synthetic.

There is no discernable power difference from Castor to Synthetic.  The main advantage to Castor Oil over Synthetic is it remains a better lubricant as it has decomposed.  Castor Oil won't make much difference on bottom end life, but it will extend the life to the top end.

Below are the colors you are looking for.  Note that the color for the plug is at the very top of the insulator where it fuses to the base of the metal part of the spark plug body, not the end where the center electrode protrudes.  The piston may be a little lighter but this is the color we found that works for us.  The exhaust will vary and may be a bit more gray.

Plug Color Piston Color Exhaust Color

Also note that the added varnish will build up on the inside of your pipe much more quickly.  Imagine how a Tuba would play with a layer of crust inside.  A two stroke is no different.

Castor Oils on the market

Pure Castor Oil like you buy at the local pharmacy is not what you want to be using.  Pure Castor is loaded with aromatic "gums" that really make the exhaust smell great, but leave a lot of abrasive ash behind.  For 2 stroke applications the Castor Oil is "de-gummed".

Many Castor Oils are actually blends of Castor and Synthetic Oils.  There may be a few types of Synthetic stocks (that would not likely be used in high performance 2 strokes)  that are not ideal to mix with Castor which is why there seems to be a taboo over mixing the two.  Commercial Synthetic and Castor Oils formulated for 2 strokes  should mix just fine together.

Castor Oil tends to decompose more quickly then Synthetic in the presence of Gasoline.  As it breaks down, it leaves more visible evidence of decomposition then Synthetic does.  Despite being de-gummed, the varnish residue it tends to leave behind further seems to evolve into a gummy substance.  If you use Castor Oil, it is recommended to mix mostly what you plan to use, and drain the fuel tank it will sit more then 2 weeks.

Many good brands are available.  Always use what your motor builder recommends.

Oil won't make you go faster.  Its a compromise between more pistons/rings verses more exhaust pipe cleaning and silencer repacking.  It has been said that Castor Oil can avoid a lean stick but we have no experience with that claim.



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