I like my 01 XC so much that I considered turning it into a Dual Sport bike. The vibration was one reason I didn't, but I am going to buy another 300 eventually and maybe do it. I already thought it out a little bit and decided to use a rewound ignition with alot of juice, and buy some rubber shimmed washers, (rubber shimmed on both sides), to isolate the motor. Wrapping a 2 stroke pipe with header exhaust wrap helps vibes, as does a carbon pipe guard with a bunch of high temp silicone between the pipe and guard. I guess you'd have to pick one or the other though, a pipe guard wouldn't fit over the exhaust wrap. Making rubber mounting points at all of the pipe fasteners also helps.
You can also fill your bars with lead shot or BBs, then fill the ends with silicone about 2" from the end openings. I've tried "Bar Snakes" from the street bike world and they help but the lead shot and silicone is better. Heavy, but on a DS bike worth it. I've seen homeade rubber bar mounts before the Flex Bars came along.
A simple thing is to fill the spaces inside your footpegs with Shoe Goo. You make a cardboard template that fits inside the spaces, then fill the pegs until just below the teeth. It cuts vibes almost completely at the pegs. You don't know how much pegs vibrate until you stop the vibes.
I rode 3 bikes that guys had done all or most of these mods to in Ga. and all were greatly enhanced. There are alot of good places to ride out in the South-East but all are miles apart, so there is kind of a cult of older guys who build really cool DS bikes, ride them several hundred miles, then ride nasty singletrack or races, and ride home. One guy rides a KTM DS modded 300 to GNCCs and Nat. Enduros, competes in B class, and rides home. I got to ride an 09 KTM 300 XCW, newer KDX 220 with some major motor work that was really fast, felt like a healthy 250, and the coolest was a 91 KX 500 with all the above mods, wide tall seat, tall bars, wide pegs, softened suspension, rear fender rack, saddle bags, great lights, blinkers, huge tank, tank bag, and a little windscreen like a Dakar bike which he made quick detach. 115 mph top speed on the 500 he said. My problem was I could barely start it with my bum leg. Then there is the crazy 55 yr old dude who rides a beat on looking KLR 650 with a 715 kit and his own homebuilt suspension to GNCCs all over the nation and finishes in the top 100 riders in long course. They call him Caveman, and he's that tough. Caveman did about half of the hardest obstacles at Red River Tx on a KLR 650. Texas Stadium, Joshua Tree, the first 2 parts of Triple Threat, Pete's Knee, The Waterfall, and some that are harder but not famous, on a KLR. Oh, and he rode it from Iowa loaded with camping gear, rode 2 days, and rode home, all in 4 days. I rode with him in Ga and it was amazing what he could do. He finished 37th overall in one GNCC on the KLR.
It's very possible to make a race bike into a very good DS bike with some innovation and even if you don't do DS many of the things I mentioned will help an old guy like me who isn't fast but rides long distance on and off road. I think having a bike that doesn't wear me out makes me faster. Paying a 10-15lb weight penalty is worth it. More that that, maybe not? The upside is you can fairly comfortably ride it many miles to a good riding spot and then have a serious bike to ride some tough trails. Or you can ride a big heavy bike that's great on the road but sucks off road. I've done both and have decided that it would be worth it to put some serious work into a light bike with a wide ratio trans like a GasGas 2 stroke. I have a DRZ 400 which I can ride anywhere my GG will go, but is sure ain't as fun in the nasty stuff. Or you can just buy a new KTM 500 for a zillion bucks and do both. I don't have even half a zillion bucks.
Anyone remember the 85-86 Honda ATC 250R Quad? It had a very smooth counterbalanced motor with plenty of power and a really wide ratio trans. I came very close to trying to put one of those motors in an 89 CR 250 frame but didn't because the kickstarter went forward not backwards, and the motor was wider and longer. I could have done it but the fabrication would have taken too much. Also the pipe was an issue but I think the CR pipe would have worked.
Speaking of KDX 200-220s, they vibrate very little. I'd say half as much as any other 2 stroke, and they weren't counterbalanced. Anyone know how Kawi did that?
I'm sure Jim Cook would remember who it was....
