So here's the poop
I've a rebuilt (well, taken apart, scrubbed, polished, and reassembled) E50 on a box standard maxi. It has a two shoe clutch with paz springs tightened almost all the way down to have the clutch lock on at as high a rev as possible. I have a 70cc airsal kit, a milled down head for a little extra oomf at stoplights (not that it helps my bulky self), A techno boss (trusty but rusty) and a 17mm bing carb on a magnum X intake manifold. Now, I have yet to take it up to full speed, but it will hold 40 all day happily.
The problem I'm having is this. At 30mph it's smooth sailing, just as it was when stock. Up near 40 though, It start vibrating like a sex toy from hell. At the end of a 20 minute ride, my feet are numb on the pedals. I'm afraid to take it any higher than 40 for fear it will shake itself apart. The con rod has less than a millimeter of side to side play, and the bushing at the tip is still nice and round. That being said, what gives?