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I ran Castor Bean Oil in my jet ski (race ski) the other I ran Torco two cycle oil in the other one. This is why I used Castor Bean Oil,, If you put Castor Bean oil on your thumb and for finger on one hand and regular two cycle oil on the other, the test I did was to wash my hands in salt water with a little sand. After it came off the Castor Bean Oil side was still slick it did not wash off The properties I believe to be better that's why I ran it in the race ski. It cost more, and had a sweet smell (like gas model air planes) was it worth the cost? I thought so at the time. But the synthetics they have now well, I think if I had a Harley Davidson or expensive car I would use a synthetic.
Once you have Castor Bean Oil in the system you can't use regular two stroke oil they do not mix.
With that said if you don't have a high performance engine. I would recommend a good quality "Marine two cycle oil" there is a difference marine oils have water inhibiters, a manufactures oil is just as good as any marine oil or vice versa. I would try to buy in bulk and save a little money. Now is your engine is just rebuilt I would run it on the heavy side (OIL) for the first 6 gallons. I think that's all I have to say about synthetic oils...