15% is overkill ( not that it hurts ) for the larger four strokers, unless you fly from higher altitudes.

All of mine fly just fine on 5%, though I typically use 10%.

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BTW: I find the Saito's easier for a beginner than the OS in the four stroke arena.

Both are great engines, but the Saitos are REALLY tolerant of grossly rich settings and will run that way all day long.

Do the same with an OS and the engine will quit, usually in flight when you throttle down for a second or two....

Typically if you can get the Saito started, it will fly that way, though not at best tune and it will consume copious amounts of fuel until properly tuned.

I've also had fewer problems with the exhausts and mufflers coming loose for some reason, on the Saitos. The OS mufflers and exhaust headers require that I drill and tap a set screw more often than not. Dunno why.