Every Road Star has a vibration at approximately the RPM
you are speaking of. It roughly correlates to the torque peak of the bike, as it occurs just below it.
Since torque peaks are different for just about every Road Star, the rpm range of this vibration is slightly different for every bike.
With EGA testing, I also saw another correlation. One that tends to explain the problem. On 99% of the Road Stars I have tested, there is a large difference in EGA values between the front and rear cylinders RIGHT where the vibration is worst. Above that rpm the combustion values even out. Below they get progressively worse coming off of idle and get the very worst at the point of greatest vibration.
Looking at a Road Star, it is opbvious that the intake portions of the mix (air/fuel) path are fairly equivalent. The exhaust seems to be making the same number of turns as well, but the front cylinder exhaust ends up making a complete 180 degree turn from its intake flow direction, where the rear does not. I suspect this may contribute to the problem.
EGA testing shows normal burn characteristics for the rear cylinder. The front cylinders however get very very lean up to and including the largest rpm of that vibration.
This means that the front Cylinder is pushing down on its piston with quite a bit more force (leaner, and more explosive mix in the front). I personally think this is the root of the problem for most of us.
Things that could potentially make this problem worse are things like vacuum leaks in the manifold, and carbon buildup in the rear cylinder's valves (which would make the rear cylinder burn less efficiently and exert even less force).
Hard to tell if this would help from your post, but I think with that number of miles on your bike, there is potential for the rear valves to be a little carboned up. Most jetting guys like to set the pilots a little rich, and given the scenario I have outlined above that would have a greater consequence on the rear cylinder than the front (remember that the front is leaning itself out as soon as you start to open the throttle).
There is a real inexpensive way to try and reduce them, that I have seen work wonders for more than a few bikes with your number of miles on them.
Go to an Auto Parts store and get a bottle of "Marvel Mystery Oil". Put the Marvel Mystery Oil into a large water spraying bottle (like the cheap ones you can get at any Wal Mart). Start your bike up on the sidestand, in nuetral, with the Air Kit removed.
Start your bike up and get it slightly warmed up, to the point that it will idle without the choke/enricher on.
Spray the Marvel Mystery oil into the carb
with the bike running. Too much at any moment will stall the motor, so take your time, and rev
the motor mildly through that vibration point and back down to idle again (while spraying). This is easiest to do with two guys working on it.
It will smoke so bad that your neighbors will think your house is on fire (NOT kidding). Keep doing this for about ten to fifteen minutes. If you have carbon built up on any of your valves, you will feel the bike begin to smooth out after about ten minutes or so. If this does anything at all for you, you can be sure you had Carbon buildup. No way to stop it, short of leaning out the jetting too much (like a stock Road Star), but at least we can do something about it.
It would be worth trying for the cost of a bottle of Mystery Oil. I have seen it solve more problems than I ever thought it could.
Also, if this does work, get in the habit of doing a Techron gas shock treatment about every other oil change. It does just about the same thing, on a much smaller scale.
GRAM<br><br>Post edited by: GRAM, at: 2005/05/31 11:59