Wife bought an 08 Nightster used with 2000 miles on it. I rode it to work one day to try it out. On the highway, at speeds roughly 60 and up, that thing has a serious shudder/vibration in the pegs that is horrible. The weird thing to me, is that it is only under acceleration... When I go to neutral or no throttle, it completely quits and is smooth as glass. I know it's not lugging because it does it at higher rpms in I think only 4th and 5th gear. This is the first sporty I've ridden so I have no comparison experiences, but my friggin calves were going numb from it!

Any ideas?

 

Did the bike have it's 1,000 mile service performed?
All Sportsters are sensitive to primary chain adjustment as well as drive belt adjustment.
My Sporty has noticeable vibration from 2,900 to 3,200 rpm under load but is smooth above and below this. This is about 59 to 65 mph. I'm lucky cause I have a tach so I know the rpm range. Run it up to about 68 to 70 in high gear and see if it goes away. It if hasn't had the service, get it done and use synthetic oil. It makes a world of difference.

 

I recently adjusted my primary and belt and at 75 MPH it's amazingly smooth, at 60 MPH it's not so smooth but not irritatingly so.
I would try adjusting both to spec and try it again.

 

I don't know it's service history from before we got it, but I did an engine and tranny change when we got it home. Check primary chain and it was really loose. It had about 3/4" of slack. Adjusted to about 3/8" to 1/2". That's what I was told to adjust it to by a coworker that has a couple sportsters. I have a service manual coming, but it is still about a week out. Hard to believe that dealers don't stock service manuals for the bikes they sell...

 

no kidding, I had to wait 10 days for my service manual.