It sounds like your high speed needle needs a LITTLE bit of adjustment.

What I do is: After the engine is running and the glo clip disconnected, I peak the engine and then back off about 300 rpms. Now, with the throttle still wide open, pick the plane up and point it's nose straight up. The engine should continue to run with little or no change in rpms. If the engines "sags" then tries to die, it is too rich. Close the needle valve ABOUT 1/16 - 1/8 turn. If the engine speeds up (most cases), it is too lean. Open the needle valve ABOUT 1/16 - 1/8 turn.

With the plane level, go to idle, then to wide open to clear the engine and repeat the test until the engine has little or no rpm change.

Things like the amount of humidity in the air and/or the temperature can affect the high speed needle valve setting, HOWEVER, it should not take more then 1/8 turn to correct IF THE ENGINE IS PROPERLY TUNED. If it is taking you more than 1/8 turn to correct the problem, your problem is somewhere else.