Your method sounds good to me.

SK ringed engines, like the 90, unlike virtually every other brand of ringed RC engines, have a tapered bore like an ABC engine. As such, they should never be run in a rich 4-cycle for extended periods of time. You need to alternate between lean and rich for cooling, but don't stay in a 4-cycle more than 10-15 seconds. My 2 SK 90s have been great engines, very reliable and easy to start. 15-6 prop is best.