The Zama C1Q-S57D is the OEM carb for the 170 and 180. It uses an "air bleed" screw for your idle adjustment and a "fixed jet" for the top end. They work best when gaskets are new, and only cost $32.95 retail from Stihl. Probably even cheaper through Ebay. The one pictured looks exactly the same as an S57D. RB-77 is the full rebuild kit. But as Dave mentioned, the Wt-194 is a common upgrade for smaller saws. Though I haven't been able to get them for $15! lol