Hi!
Agree with DR 1Driver; You have a too large prop!

Highspeed needle should always be set with the throttle drum fully open. As Dar said, the low speed (Idle needle ) will interact too much if you set the highspeed needle with the throttle drum not fully open...which is no good! Second: What happens when you open the throttle drum fully??...then the mixture gets upset (Engine runs lean) when too much air is entering the engine.

Regards!
Jan K
Sweden