1. LOAD test the ignition coils. Inline spark testers are a total waste of time and money. They do NOT duplicate a real cylinder under compression.
2. Pressure test the carb needle and seat.
3. Remove engine cover down to the flywheel. Remove all dirt, grass, oil, bugs and so on off the engine cooling fins and engine block. Look under the flywheel and behind mufflers ect.... Block and fins should resemble a new engine. This is a YEARLY maintenance item in ALL air cooled, small engine manuals. Neglect this and you are asking for engine damage.
4.Check for vacuum leaks around intake tubes and such.