As Jon says clean clean clean those connections . Also worth checking out is the earth cable from the battery to the frame/engine. Mine had a bad join where the terminal was crimped onto the cable right at the battery and I bought a new battery and starter motor brushes that I didnt need before I twigged ( actually some body told me almost exactly where to look ). When starting became sluggish I blamed the battery and used jumper leads to start it off another battery so I bought the new battery ..... no better .... new brushes ... no better , but every time I jump started it ... no problems , starter wound over great. I had been connecting the earth jumper lead to the footpeg bracket ...... thus unwittingly bypassing the faulty earth lead..... ho hum
and it ain't no harley. Not that I have anything against a harley 
they are not interconnected. thanks