I tune mine by the pinch test and listen test backed up by a tach. I'll get it sloppy rich at full throttle and close the needle till I get max rpm by ear then open the needle till I hear a drop in rpm. Then I pinch and release the fuel feed line and listen for a rise in rpm, done. If the rpm drops it's too lean. I'll usually back this up with a tach at least once per flight day so I don't screw it up too bad. It smokes just a little.

Are you using synthetic or castor based lubes in your fuel? I think your discoloration may be related. A friend had an OS FS52 mounted inverted that he ran only castor through and the head and exhaust got really nasty looking. Hard to get off too. I know, it's now MY engine! I've been running synthetic Byron's or Morgan's Cool Power through my engines and have no discoloration to date...

Any long term problems to look for on my SS'er?? I'm gonna do the landing gear thing before it's first flight with a Sullivan tail wheel assembly. My engine choice is either going to be my 50SX or one of my 46FX's. The FS52 is just too nasty looking. It needs to be in a cowl. Hmmm, I need another plane. Cool!