I'm having an issue with vibration at idle. I have an 09 Road King with 17,000 miles on it. This also is something new to me. I have had it checked by an Indy and he can't find anything loose in the motor mounts. When the rpm reaches idle aroung 950 the handle bars really shake. I've replaced the spark plugs and the wires, no love. NBo problem at speed or if I run the rpms upn to about 1100. I'm not thinking it's a huge problem, but it is annoying.

 

When my bikes idle gets down to 950 the shake is pretty bad. bring it up to 1000 and much smoother. It seems to go sub 1000 only when sitting in traffic and warms up a bit. While at running speed, smooth as silk, except for the vibration on the floor boards. Its more of a tingle.

 

I have had seemingly "rain related" vibration several times this year. And it wasn't very subtle.

The first time I thought I'd actually broken something, it came on so fast. I stopped at the nearest gas station, looking for any sign of a problem, wheel bearing, cracked swing arm whatever. I found nothing. Started the bike up and checked everything at idle...Nothing.

Got back on the road and it was gone.

It's happened a couple of times since then, only on wet roads at about 50 mph. It always goes away. I'm wondering if it has something to do with the E-3 tires, just don't know.

The bike gets 400 miles a week commuting, and cleaned/serviced every weekend. Everything appears fine.

 

Check your right hand slip-on, on my 2012 FLTRX for some unknown reason it loosens and moves back until it contacts the hanger. I then get the vibration from the footboards, like someone said before loosen the entire system but do not remove the nuts and then tighten starting at the rear and work your way forward.
I have the V&H PowerDuals with stock slip-ons, not sure if the problem is the rubber hanger bushing or maybe I need a new clamp at the slip-on/header connection. Anyway re-positioning the right pipe does the trick for me everytime, at least no vibrations for a while.