single cylinder engine will vibrate (yus - even the wonderful 4stroke lol), often times it's not actually just the engine running that's at fault. The number one cause of excessive vibration is the stock "rag joint" style rear sprocket mount and overall chain alignment, while ofc you can get it "pretty close" there's simply no way to get it perfectly aligned.
An aftermarket sprocket adapter that clamps directly to the hub or bolts to a disk brake mount would do wonders, as would a shift kit if it's in the budget, making sure your front and rear drive sprockets are as close to perfectly aligned is a must in any case.
Another source of undue vibration is the "tensioner" - even IF it's actually been bent to be inline with the chain and not the chainstay - it's still a hard plastic wheel that tends to chatter as the chain links travel over it. Doing away with the tensioner if you can or making one with a skate wheel would help - see this thread for some ideas: http://motorbicycling.com/f11/chain-...ons-11815.html
The typically low-quality chain that's included tends to be a touch twisted and with a few binding links - there's another source of much vibration. Replace it with a quality 415 if you can find it, a 41 if ya can't - usually available at any good hardware store. Rule of thumb - quality
chain isn't cheap, while you can find 41 and even 415 "heavy duty" chain for anywhere from ten to twenty bucks fer about 10' or so - don't be fooled by the label, it'll prolly be quite significantly better than the stock chain... but it sure as heck isn't "quality" lol True performance chains can run up to a hundred bucks, but that's no doubt overkill heh
Yet another source of the bad shakes is a poorly tuned engine, while many of these 2 strokes will "4 stroke" when not under load and/or still being broken in (misfiring), often it's a simple case of running too rich and/or poor ignition. Replacing the plug with a properly gapped NGK B5HS or B6HS (.025-.030 gap), running it for a while at speed and checking it's color (after cool down ofc), then adjusting your air/fuel mix accordingly (needle clip setting) should help quite a bit.
Here's one that's often misunderstood - attempts to dampen felt vibration by using soft rubber shims, wraps or any other means of isolating the engine mounts from the frame will in actuality INCREASE vibration and can lead to premature fastener failure. Not only will the vibration of the engine wear/cut through the padding in a matter of time (leading to "loose" fasteners as well), these engines simply were not designed with soft mounting in mind. With only two points of contact and both of those quite low - there's just too much leverage to be anything other than hard mounted. There's been some success with hard
polyurethane mounts - but that entailed a mount redesign and some welding - the typical "chunk of innertube" method is a recipe for eventual disaster.
When it comes down to it, a properly maintained, tuned & mounted kit really isn't that bad - adding in some quality street tires, gel grips and a soft, sprung seat takes care of the inevitable vibration of a single cylinder - throw in a set of front shocks and yer stylin'