I loaned a used K&B .61 (first mistake) to a friend.
He put a plastic spinner on it, which turned out was
out of balance. The o-ring on the low speed needle
was weak (but ok), and during the flight the needle
vibrated and turned in (lean). He was running it wide
open....and the thing gradually leaned out until it seized.

As you can see....the ring was stuck, and it was fried
BIG TIME. I put a good used piston, ring, and liner in it.

(and a new o-ring)