Zingers run slower due to bad airfoil shape. Look at the leading edge and trailing edge of the blades. Both are square unless you worked on them. YS engines will quit with a bang and usually kick the prop off. If you are using a spinner, make a couple discs of 80 grit emery to put between the spinner bp and drive washer. One with grit facing the drive washer, one with grit facing the spinner bp.