Stick to the cessna, it will teach you a lot more than your trainer did, but I think your not ready for the spacewalker yet. Plus it will give you the time to learn four stroke tuning on something smaller with out fear of cooking the bigger .91. Get a tach, it's the only thing you can use to set your four strokes. Hard to judge 8500 rpm from 9500 rpm, if your use to two stroke sound. The cessna will,teach you sink rate and stall characteristics