It does sound like you have a air leak. If you are tuning the high speed needle to the point were it's going to come out and you are running those temps then there is a air leak, that is way to rich on the hsn. you should start from factory settings and turn the hsn clockwise. To check for a air leak do the simple things first.

1. check fuel and pressure lines for cracks or holes
2. Loosen the carb binding nut, remove aircleaner and press down on carb and retighten the nut, sometimes the carb is not pressed in fully.
3 Submerge the tank in water, blow into one of the lines squeezing the other so air can not escape. If you see any bubbles coming from the tank then the tank has a fracture.

If theese simple things dont produce any results then you will have to pull the engine out and seal the carb and the back plate. Have you noticed any fuel around the backplate or the flywheel, if so than you have a bad bearing in your engine (another culprit of airleaks)