It sounds a lot like an air leak in the fuel supply. I'd start with the simplest first, replacing the fuel lines, both the pick up line in the tank and the supply line to the carb.

Then move the search to the carb: disassemble the needle and check the O-rings for fidelity. Replace any that are not perfect. Also check the O-ring that seals the carb body to the case

Then take a look at the backplate seal. You may also have a bearing air leak but that's a stretch...

I forgot to mention that if you have an air leak that happens after some fuel burn, then the pick line in the tank is suspect. You might be able to see the air bubble in the delivery line to the carb