I thought I'd post this to see what you people thought. Last year, we re-built a '96 XR600R, making it a 629, valve job with new valves & bigger springs, and we removed the auto-decompresser from the cam. This year, the spark plug got accidentally cross-threaded, so we took off the head to heli-coil the spark plug hole. While it was apart, my cousin decides to port & polish the head. He did it himself, and did a great job. Also, he fadricated a stock WR450 muffler to fit on the XR600. Again, I can't believe how good it looks. So anyways, we put the bike back together and fire it up with the same jetting as it had before. I'm not sure of the pilot, but the main was a 170. With a little throttle, the headers started to glow, almost instantly. Figuring it's too lean, we try up jetting it. 172 - Headers still glowing. 175 - Still glowing. 178 - still glowing, but not near as quick. 180 - still glowing, but again, not near as quickly as before. Keep in mind we live in CO, and our base elevation is 5200 ft. It just seems crazy to me that we opened up that engine so much, it needs this much fuel at a high elevation. We didn't have any bigger jets, so we quit for the night. Can you guys believe that this bike wants a 182 or 185 main jet? I was wondering if anyone else has done similar mods? Does it seem right to have that much of a gain in fuel needs? The other possibility we thought of is that the stock headers are too small for the ported head & new exhaust. How many people think this bike needs bigger headers?