I put an OS 7D carb on mine; you also need to use an OS adapter part no. 22022014 with this carb. I'm running 10 or 15% Cool Power fuel, and a stock Bisson muffler (both outlets open). I use an APC 16X8 prop, no rpm figures. The carb changed this motor completely; it's dead reliable, starts quick and makes great power. I'll add two points to the above posts: This engine takes at least two gallons to break in (noticeably better transition), and it's very sensitive to the low speed needle adjustment so take the time to get it right.