I recently had it with my '98 xr engine I had stuffed into the XL frame and rode east to west coast with. Its timing chain went slack on me and it ended up running rich and nasty. The last straw was the choke lever falling off while I was in downtown Portland, leaving me to a last resort of ripping off my homemade intake made of plumbing parts and k&n, and stuffing a hoseclamp sideways into the throat of the carburetor to keep the choke flap open, and blasted home with the open intake (no filter). I'd had my old XL engine (low mileage head, bad tranny) sent to me. I put the dual carb head back on, the timing gear for the wider timing chain so I could use the one from the XL, the kickstart shaft for it's decompressor cam along with the corresponding side cover and cable, as well as the original airbox, as the frame was designed more for that kind of setup with the shock being in the middle. I'm not sure if it was the fact that I had fixed the bad valvetrain or just the better carburetion, some combination of both I'm sure, but having the level of power that I did after so long was great. Going 50 and want to be going 80? No problem! Tilt your wrist back a couple inches and wait about 3 seconds. It's been a while since I tested the single carb versus the duals, but I think the duals have it over the singles for sustained upper end power. But the low end has a lot more "balls" now too, but that's probably entering the territory of just how crappy it was runnng before. The piston had a small dent from each valve, I guess the timing chain was that slack. Another cool thing is that the wider timing chain of the XL engines, as opposed to the the narrow XR and XRL timing chains, makes the cool whirring sound, I missed that and I know where that sound originates now.