Sport pilot sport pilot sport pilot. Why do you think it will detonate..... This engine will turn a 14 or 15 inch prop around 6000-7000 rpm 6,500 on mine and I used 10% fuel and a get this an old OS number 3 plug...... maybe my engine is just a special one.
Most assume you must turn the engine at a rpm that is normal. FP type engines have very low timing and small carbs so think about that for a second. I have seen OS 26 four strokes turn 15 inch props also at low rpm and run for 15 minutes on two ounces of fuel. Now with the OS 26 you couldn't open the carb all the way but a hair over half was good and it flew the plane it was designed for (old timer) very well.