It is best to tune a 4 stroke with a tachometer; the variation in pitch from lean to rich is not as noticeable as a 2 stroke (I've not yet fired up my first four stroke, but did work with my trainer on his and got a little experience).

Read the instruction manual. If any adjustments need to be made, they are not difficult, and the engine comes with a gauge and the tools to do the adjustments. OS four strokes have the reputation of being very easy to run, and running right out of the box. I wish I had one (in the Super Stearman I don't yet have).

I say get the four stroke, and in the mean time download the manual and read it a few times.

I love OS engines and really can not wait until (they come out with a 1.50 four stroke and) I have one.