[hardlydangerous]

regardless the sync of you carb affects the idle circuit, and wont cause it to bark black smoke. thats an overly rich circuit.
most often stuck or sticky throttle slides, slide caps installed incorrectly, slide springs popped out of the seat....holes in the vacuum slide to low of needle clip position, to low of float level, too big of main jet, too far out on the mixture screw etc etc

[750head]

Hi guys, I got rid of the black smoke with all your posts. But now I don't have any power and it sounds if it only runs on three cylinders. Yes all four plugs got spark.