RE: What size 4 Stroke for a 40 size trainer?
I would recomend a O.S. 46AX two stroke for a trainer due to its power, ease of use, and most importantly, the price. Now if you have your heart set on a fourstroke, I would go with a saito .56. It has good power
and should be very similar in weight as your average 40 size twostroke.