Put it in first gear, then try to push it back with your feet. Is it hard to do so? If so, it's probably related to the clutch.
My bike did this the last time I hopped on it and it definitely seems like it has something to do with the clutch. I haven't completely fixed it yet, I just increased the idle RPMs a little bit for now.
Question for MERCURY (Hope you don't mind Vulcan16):
How does a tight cable cause this? Shouldn't it be a loose cable that would cause the clutch not to disengage enough, hence leaving some friction to slow the engine down? I'm really wondering about it, cause if a tight cable can cause it, that's probably my problem.
1985 VN700 unknown mileage (over 33K)
Iridium spark plugs
NGK wires and caps