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Message: [QUOTE="TexKDX, post: 143857, member: 16276"] mtngoat, Gary Hazel at Thumper and I had a long talk about all this stuff. Also a local guy here has dropped over $2k on an XR250 motor trying different hop-ups. What I am about to say is from the experience of others, not me, but seems to be of some help here. Gary said that the higher lift, longer duration cams cause all kinds of problems. Rockers get eaten up and seat life is shortened due to the slamming closed of the the valves in comparison to the stock cam. Even with hardened rockers the problem just moves around due to the increased stress caused by the cam. Longivity the XRs are famous for goes out the window. The other guy has finally settled back to a 290 bore (very thin liner but he already bored it out), stock cam, stock carb, ported head, and the adjustable cam drive gear. The adjustable gear lets you compensate for cam chain wear plus move the power around some by changing the cam timing. He was never happy with the pumper carb's throttle response, even though the extra flow did help out when he had the hot cam in it. Now, I must confess, even though I planned on keeping this a secret. I did a XR250 big bore a few weeks ago. Went with the 10.3:1 (stock ratio) 277cc JB piston from White Bros. Cost on the kit was $95, the base gasket was $7, and it cost me $60 to get the cylinder bored, honed, and chamfered. Another $20 for rush shipping and my labor, so for under $200 I have an XR280. Other mods are just the usual pipe grind/baffle extraction/snorkel removal/jetting. I flat love this bike, let me tell ya. New springs are in order as it packs down in the whoops at race speed, but overall the bike is awesome. Never would I have imagined that the little XR would be so fun. The 277cc piston represents about an 11% increase in displacement. Quite frankly I question the XR400's 415cc mod - just 4% increase in displacement? Seems like alot of work to me. Having owned the WR400, now the XR280, and ridden about everything that burns petroleum, I have a hard time understanding why someone would drop a bunch of coin in the XR400. It does not have that light feel the 250 does, and its 400 class competition is SO good in stock form. Not to say the 400 is a bad bike, it is not, but perhaps is the one that should most be left alone and appreciated for its attributes. The under $200 big bore kit for the 250 is a no-brainer and best I can tell does nothing to effect durability. The cool thing is the non-Nikasil barrel makes this possible. Beyond that though, I'd say look for a different bike like a DRZ. At one time alot of this work may have made sense, but maybe not so much sense now that the WRs, DRZs, and KTMs are available. I picked the XR because I wanted no radiators since I do trips in Mexico and did not want dropping it on a rock to end my ride and leave me 1,000 mi from no-where. It only takes 15 hp to go 75 MPH, so the 280 making 24 or so ponies will pull me and my gear fine on those rare pavement sections at 60-70 MPH. The 280 does not roost, but it does reward and promote a smooth riding style. Good luck on picking the right mods for your XR Traylrider42 and let us know how it comes out. [/QUOTE]

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