arcing across head to expansion chamber

[SpecializedMountainMoto]

I noticed tonight a small arc going across my head to my expansion chamber, keep in mind it is very tight between the two only maybe 20-25 thousandths. why would this be happening? Bad ground or is the spark running throughout the head, its a fred head

 

[maniac57]

Adding another ground cable from the frame to the engine is never a bad idea

 

[crassius]

spark should only be inside the chamber - outside means bad plug, bad boot, or bad wire