motorcycle idling _Very_ fast?

I have a 2006 Kawasaki Vulcan 500 with about 1300 mi. This bike was not ridden for probably at least a year by the previous owner. I bought it, rode it around probably about 100 miles with some Lucas additive thinking the idle would smooth out. Yesterday while riding it started sputtering and backfiring; then the bike revved to high RPMs and would not come down. Now when I start the bike it immediately goes to high RPMs with the clutch squeezed in, 1st, 2nd, 3rd gear, etc. Seems to be ideal for going 35mph or higher (I rode it the last 4 miles to home).