LB Sticky Air Vane Questions

I ran a tank of gas through my fine 10550 LB this weekend and after a break and a re-fill, I cranked the 'boy and it ran at about 1/3rd throttle and a bit rough! Being careful, I reached in with my finger and touched the governer air vane and the Duraforce came to life - yippie!

My question is - what causes this? Do I have a weak spring or can this be caused from dirt/grime over time? I hate to put a drop of oil in such a dusty place.

Looking for tips/suggestions.

Thanks in advance!
Bill