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94 xr600 38mm fcr conversion

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Have just fitted a 38 mm fcr carb to my 94 xr 600 thats on first oversize with base gasket remove, head flowed, fmf powerbomb pipe and fmf t4 muffler. We machined up a nylon adapter that has an offset hole machined in as well as 2 holes lining up with the small holes in the bottom of the carb. Next the rubber inlet manifold had approxiamately 3mm shaved of the lefthand side of it so it has a tapered face, just get carb to line up in the frame and to the airbox, We also had to pein the frame in about 2mm to give the carb clearance. This was done carefully with a ballpein hammer and painted over, cant even tell. On the inlet side of the carb I hose clamped a short piece of rubber tube to it and slide the adapter inot it so the small holes in the bottom line up, and clamp the other end up. Do these two clips up really tight because you dont want them to move, and maybe put tape around the clamps so nobody inadvertantly undoes them. The the other end of the adaptor slides into the standard airbox, and the throttle bottled straight on using the standard crf 250 cable. Bike started easy, and mate adjusted idle and air bleed, then I did a test run which made it way more responsive, but flat top end, so we replaced the 135 mainjet, with a 130 which made it better but it was starving for fuel if the throttle was cracked at half throttle, dropped the clip on the needle down to 4th groove, now its a rocket, pops the front wheel up easily in 4th and hit 90 mph a lot easier. Jetting specs may vary depending what you have done to your bike and what elevation you ride. To me its a must do.

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The shaping of the rubber inlet manifold was to shift the carby inward toward the frame, or outward away from the frame?

On my XR600, I used XR650L rubber inlet manifold and air box boot, which position the carby outward away from the frame.  So my carb does clear the frame, but makes slight contact with the fuel tank.

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The shaping of the inlet manifold was to get the carb to clear the inside of the frame. Also made a gasket for the manifold after it was shaped as the original seal in the manifold was ground away while shaping the manifold. I used standard xr 600 airboot.

 

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