I had vibration on my 1997 Sprint Sport. It came through the right hand grip & became intensely painful on runs.
It was moderately high frequency (felt slower than engine revs & faster than wheel revs - see posting from Metro DC above). It was of small but noticeable amplitude, got bad by 70mph & never went away. If I was "trying hard" I forgot to notice it but as soon as I had miles to cover & held a steady speed I noticed it alrught.
I put it down to bad handlebar angles & old bones (me).
The a mechanic suggested I had a loose bolt on the sprag clutch & alternator drive shaft.
He was right. The shaft is splined along it's length with no step, so a loose bolt on one end makes the other loose as well. The bolt was actually sheared off and both drive gear & alternator drive cup were happily rattling around on the shaft.
Curing this sorted the vibration and made the engine much much smoother. It made it so much better I almost kept it, but then I test rode a Speed Four. So it had to go.
Incidentally this is not an easy job. Stripping fairing, coils & carbs is routine for almost every job on the Sprint. Taking the clutch off is not hard if you use the rear brake & a friend. Forcing the new drive shaft through held tight up-against the old one (to avoid washers & spacers falling into the sump) is nerve-racking but okay. BUT Putting the clutch centre back through the clutch & oil-pump/alternator drive gear woudl try the patience of a saint. If I ever have to do that again I will drain the oil & lie the bike on it's Left side so that the gear stays in one place & in mesh as you thread the clutch centre through.
Hope no one else has this problem & if you do I hope this helps
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