The high needle is only active above 1/4 throttle. The low needle is always active. 

Idle mixture

1.  Open low speed needle 1.5 to 2.0 turns
2.  Open high speed needle 2 turns.
3.  Start the engine at slightly high idle rpm and let it warm up.
4. Adjust the idle needle (closest to the engine) for best rpm
5. High speed mixture:
        Slowly apply full throttle. If the engine stays too rich, close the high needle a bit so the rich condition is cured, but no more than that.
   This is the basic high speed needle setting, at which the engine will run without damage due to lean mixtures.
    
   Midrange (warm the engine up to  operating temperature before doing this adjustment)
    
   Apply full throttle
6. Adjust for max rpm
7. Slowly reduce throttle until the engine starts to four stroke. 
8. Lean high speed needle until the 4 stroking stops.
9. Go back to full throttle, and adjust for max rpm, 
10. Open the needle 1/16 turn and throttle back again. 
11. Repeat the above steps until the engine runs well at any  RPM.
12. Check for crisp throttle response. 
13. If the engine lags open the low speed needle 1/8 turn.
14. Let the engine idle for a couple of minutes 
15. Repeat steps  12, 13 and 14 until a crisp clean transition is obtained. 
 

Don't worry if after adjusting mid and high range that the engine does not  run totally smooth under 1/2 throttle especially with a magneto  ignition.   

Run the engine about five minutes and check  the plug.  It should show a light brown or sand like color..