Pretty good sign of an airleak when you make some pretty big tuning adjustments with little to no results.
Places for leaks - backplate,carb neck and pinch bolt. Be careful with carb pinch bolt, you can tighten these enough to crack the carb body. Also the backplate joint that needs sealing is under the ezstart/PS, not where the oneway is located. Use either a purpose built engine sealer or O2 safe hi temp rtv. Use as little as possible to get a seal.