The part I'm referring to is circled in red in the picture. What exactly do these metal rings do? I bought my yz a few months ago, and when I did the top end rebuild, thone rings weren't there. I've been told that they can kind of adjust the power curve of the bike, and I was wondering if this is true. I have the metal rings, and I'm thinking about putting them in and seeing if there's a difference. Has anyone noticed a difference with or without them?