Curious if someone can help me here: Last week I took the bike out, it was about 60F out and low humidity. The bike ran absolutely great. I put a solid 1.5 hours on the engine meter and was really riding the piss out of it. Took it home, cleaned the air filter, changed the oil and put her away. Fast forward to this week: Same buddy and I go riding. We go to the same place, and at 6am, it's the same temperature. The bike kicks over nice and easy as it always does and off I go. I immediately notice it's surging like mad through the mid-range and popping more than normal, etc. I ride it for about .4 of hour (in total), to get it back to the truck. My buddy puts his hand behind the exhaust and it melts his glove. We shut the bike off, load up and go home. We first check the plug, hard to tell here -- after hours on the the plug before, a mere half hour in it's shitting-running-mode didn't show much. Next, check the valves. All five are spot on within spec. Next, clean the carb and check all the jets. No problems with any jets. Put it all back together, start it up, and it does exactly the same thing. You could hold the throttle still (in the garage) and hear it stumbling/surging. It also got hot enough in literally 30-45 seconds of running, that it started pushing coolant out of the overflow. The bike is not eating coolant, or oil. The air filter is clean (new as I said). The bike has a slip-on, stock header. When I checked the valves, the notches to line up TDC-C were perfectly lined up and the valves were spot-on, so I don't think it's the timing. Suggestions? I'm obviously thinking jetting, but why would it run great for 2-3 hours of total engine time, and then all of a sudden start sucking ass? I'm trying to eliminate other options before I start screwing with the jetting, because it really did run great before today... Thanks in advance.