Oops, made a mistake - my bigger AX says 2.5 to 3 turns open, 46AX says 1.5 to 2 turns open.

Make sure you are two FULL turns open, and not two 'half turns' open; common mistake.

Sounds to me like it's starving for fuel assuming it's going down to almost quitting. Is it a gradual increase and decrease in RPM, or is it going from WOT to almost dying and back up again?. Check your fuel lines, including the ones in the tank, make sure the clunk is free in the tank, etc.