What is this Black ring like thing around the high-end needle ? It is removable and just slides in. Is it for holding the needle adjustment in place? What if i dont use it? I removed it to remove my engine since it was hitting the wood, When I put it back I dunno how tight the bent S shaped part be...

Also parts of my plane's wooden engine area are reddish /pink in color. Is the wood reacting with fuel...? not sure if it was when I bought it..also at that time everything was new to me(still is LOL)

Pls advise...thanks
-747