The stunters are presently running 25% oil in the OS LA series of engines. The reason for so much oil is that it promotes good 2-4-2 breaks. That is because it pollutes the incoming charge better than unburned fuel because it is thicker and doesn't burned, thus an engine will 4-cycle at a leaner setting with more oil, and break out of it quickly. I don't think the liners are any softer than other manufactures, all of these old steel lapped engines used soft steel on the liners. McCoy were probably softer than Fox. I have used Morgan's Coolpower with 4 oz of castor oil added with no problem on my Fox .35. Though this was only for several tanks, the compression does not seem any worse. I am now running 26% synthetic-castor mix. It breaks into a two cycle much crisper now.
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