Originally posted by allenclarkson
A fellow named Don Eilenberger rode an '85 for a long time - gave it the name Finest Year K or FYK and they are fairly widely known now by that handle. The '85 had many unique features - different seat, different pegs, different cams and compression and on and on. If you get it running good, it should give the Cobra a run for the money.
And he once in a while looks in here since he was appointed as a moderator..
Don's a serious gearhead and worked out ways of reducing the vibration - not eliminating, just reducing. You could ping him at email@example.com and ask his advice. If you want good advice from him, my advice is to make the questions very clear and put each question in a separate paragraph - makes it way easier to respond. My guess is that he may have a set of recommendations written up to send on. I do remember two of the things were to be sure the rubber shock absorbers in the alternator drive are fresh and to check all the exhaust system attachements from the head to the exit. There were more I don't remember.
The exhaust is important - and it is mounted differently than later years. Make sure the rubber mounts at the rear attachments are in good shape - you might consider replacing the rubber donuts.
Also - a GOOD tuneup is helpful. You want the engine to be running as smoothly as possible. Valve clearances should be dead on. Do not futz with the inter-throttle-body linkage - you'll make it worse that way.
Check the fairing for places it may be vibrating - I added rubber in several spots that help keep it from resonating with the engine.
Replace the rubber mounts for the handlebars - these harden up and transmit vibration to the bars. Also - if it doesn't have them - get bar-end weights.
Finally - it's probably worth retorquing the frame to engine/trans bolts - there is a specific tightening sequence shown for the '85 models in the factory service manual. It also is different than the sequence shown for later year K100's
And if you ride it so the RPM's aren't lurking around the buzz point (which was right around 60MPH) - it's not bad.
Wait, before you do that, check the IBMWR K tech list at http://www.ibmwr.org/ktech.shtml. At the end of that page you will find his advice on checking out '85 K100's before purchase - too late for you but you might find useful stuff there anyway.