I posted a reply to this thread fairly early into it complaining about a vibration. The bike had 30k km's then and has over 40k on it now and I don't think that it has gotten any worse but is still slightly annoying. I have gotten into replacing the clutch (to handle more horsepower) and have checked everything fairly carefully and think that I have an explanation for it (the vibration). The first thing I did after removing the clutch plates, was to mount a dial indicator between the input shaft of the transmission and the outer clutch basket. There is about 20 thou movement between the two but what is interesting is that there is more movement down (15 thou) than there is up (5 thou). You would think that gravity would would pull the basket down and the opposite would be true. I then realized that the anti-judder spring "pushes" against the basket in an upward direction. So, if there was some imbalance in the clutch basket, it would produce an outward force proportional to the rpm. My theory is that around 2500 rpm this force plus the force of gravity overcomes the pressure of the anti-judder spring and now the basket moves down when the heavy part is down and then back up again as it rotates upward creating our vibration. As rpm increases, the centrifugal force from the imbalance is great enough to overcome the spring pressure no matter where the basket is rotationaly so this up and down movement stops and the vibration goes away. When you put some pressure on the clutch lever it pulls the basket forward causing it to run true. I'm not sure if I'm explaining this very well but in essence I'm saying that below 2500 rpm the anti-judder spring keeps the basket running true and above 2500 rpm the imbalance keeps it running true but at 2500 it is moving up and down. To further substantiate my theory, after removing the basket, it doesn't look like it has been balanced at all as there are no drill holes or weights that I can see. Also, take a close look at the anti-judder springs in the picture. There are some that are much thicker (ie heavier) than others.
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I then mounted a shaft in a vise and placed the inner bushing on it and the basket on the bushing. It definitely has a heavy spot which turns to the bottom as you rotate it which means that the amount of imbalance must be fairly large. I'm surprised that there isn't more vibration just from the imbalance. Could this lack of balancing be intentional or an oversight? Not sure. And why does Triumph use 4? different springs.
