RE: low speed needle
A few more details would help.
Why did you change it? Had it been running fine and then started to act up?
Which direction did you move it?
How far?
Which engine, prop, glow plug, and fuel?
Did you reset the high speed needle between each low speed adjustment?
How much fuel has been run through the engine?
All these details are important to be able to try to point you in the right direction.
Brad