Having jetted my Puch Maxi (techno boss, stock #4 cylinder/piston, head milled to fins, tightened clutch) so that it's running perfectly on all plug chops, I'm still getting tons of blackish smoke from the tailpipe. My transmission fluid level hasn't been changing, so I can only conclude that it's coming from the engine itself. It's quite curious. The bike runs very happily, it's just stinky and smoky. More so than it was last year when I hadn't raised the compression or adjusted the piston shape.