If the plug is black it is too rich. It is very possible that it is overfueled too the point that the fire is still burning when the exaust valve open and keeps burning right down the exaust pipe. A white insulator on the plug signifies a lean condition along with melted/seized pistons in extreme cases.

 

when are your pipes glowing red,, at idle / adjust idle mixture screw,, with part throttle / put a bigger piolet jet,, half throttle / go down on your neddle,, and 3/4 to full throttle / put in a bigger main jet.... take the time and look at your pipes in each of the steps above to isolate your trouble.. then make the change thats needed.... works great for me.. hope it helps you out..... ps if you dont hear ticking leave your valves alone..........