Welcome to the wonderful world of Evolution! When an engine doesn't respond to the needle valve changes consistently, there is another problem. I'd look first for an air leak. The carb o-ring, backplate, and fuel lines are the most likely culprits. An air leak can cause that up and down running condition as the engine cycles between rich and lean due to the way the leak happens. Being set slobbering rich is probably part of the issue as well. I had one that had to be set crazy rich just to stay running and would go up and down like you're describing at full throttle. If I tried to lean it out, it would snap straight to too lean and die. It had a bad front bearing from the factory allowing it to suck air.