Motorcycle Questions? Ask a Mechanic.
It definately sounds like there is a connection issue somewhere. I would first try removing your main power and ground cables, place a multimeter lead at each end and move the cable around while monitoring continuity. It is possible that there is some corrosion or damage inside the insulation of the wires and the vibrations could be making and breaking continuity.
It should be somewhere around the primary or starter. I would not recommend adding a new ground. Be sure all of you engine mount bolts are tight as well. The main fuse is a great area to check, I would replace and check for corrosion.