Use what is readily available to you.
As you have probably already learned, some oils do not play well together. PAO & PAG base stocks repel and can cause catastrophic damage.
If you know 100% certain what was run in the engine previously, you might do well to stick with that. If not, then flush the crankcase thoroughly (you can search this forum to find a variety of methods and preferences for that) before changing to a different oil.
I really like the Briggs 4T oil, but any good quality oil will suffice -- they key is to keep the oil clean and fresh in the engine. Aside from a magnetic oil drain plug, you have no filter on these engines to pull metal or contaminates out of the crankcase.
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Thanks and God bless,
Brian Carlson
Carlson Racing Engines
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34 years of service to the karting industry ~ 1Cor 9:24
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bcarlson@CarlsonMotorsports.com