JDW, mine may be different as I do not have the spring to keep it loaded inward. I have two of these motors and checked them both out and neither have the spring. These are the .40 size. You were right though the throttle ring bears against the rotor so it does have no effect. My bad. I was playing with them again last night and noticed the problem again and checked it out to find that the throttle ring does just butt up on the rotor and does not fix the problem.

There just seems to be too much slop on the machining of the rotor where the screw holds it in. This seems to be a problem on both of my motors. I checked my Super Tiger, SK, K&B, and Irvine motors and none of them have that type of slop. The K&B has more slop than the rest but not over .001 of movement. The GMS has between .0015 and .0025 of movement when checked with feeler guage. Not sure how much of a problem this is since it is so minute.

I am going to go back this afternoon and try to re tune like you stated with the idle mixture. I did this the day before yesterday and thought I had it but tried to get it a little better and went too far and my glow starter and starter's batteries were dying so I could not get it to re start. I was setting at approx 2 turns out on the idle setting and 3 turns on the main high speed needle. I believe the 3 turns out is the factory spec. I will have to find the instructions this afternoon before re trying.