9n and black soot in exhaust pipe

OK my rebuilt 1943 9N is running pretty good, but I noticed a lot of Black soot on the inside of tailpipe. My guess is the gas fuel mixture is a little rich, which way do I turn the screw to lean out the mixture?

nathan........heres how you adjust yer carbie. Set the down-pointing MAINJET to 2-turns and LEAVITT!!! Adjust yer side-pointing idlemix fer FASTEST idle NOT SMOOTHEST idle. Understand the difference??? Usually will be 1/8-1/4 turn. To answer yer specific question, yer idlemix is BASS-ACKWARDS, out fer LEAN, IN fer ENRICH. Set yer behind the throttle idlespeed for ennythang under 500-rpms. I once gott my eazy starting 6-volt 8N to idle 375-rpms with transistorized tachometer after I rebuilt the carbie. I know yer 9N don't have a tachometer, but make a WAG (Wild-A$$-Guess) ...or... squander $20 (cheap) fer battery operated tachometer atta HOT-ROD store. (tip: ask the clerk) They may object but most 12-volt tachos will work on common 9-volt battery. Oh yeah, yer 9N is timed on the kitchen table when you replace the points (0.015). Yeah, theres an external timing screw (4-deg) that was designed fer back in the days of NO-LEAD gasoline. As I said, timing when you replace the points. One last comment; DON'T even thing about PERTRONIX transisorized ignition. They don't fit inside yer 4-nipple dizzy.......HTH, Dell, yer self-appointed sparkie-meister

Clockwise. Here's the procedure from the manual.