Well, today was the first ride of year and I got to experience something new today, boiling gas. I was riding behind my wife, mostly in 1st gear for the afternoon, riding approximately 15 miles with frequent stops. Weather was beautiful at about 75 deg F in Michigan, with low humidity and elevation of less than 1000 feet. We have ridden this trail MANY times under much warmer conditions, with the same jetting with the only issue being the coolant boiling over occasionally to the reservior. This is not a jetting issue. I ride an '01 WR426 with WR timing, free mods, JD jet kit, and Vortip. I know my bike well, and how it reacts to temperature, humidity, trail conditions...etc. At one stop, I heard the gas hissing out the tank overflow, and saw it running down the front fender. I pulled the hose off the gas cap and it was spitting and sputtering. The ball-check valves in both the gas cap and the one on the overflow tube wiggled around so they were not bound up. The coolant never boiled over once today. I searched, and found that there are a few possibilities for why the gas was doing this. 1. bad gas cap 2. overheating, heating the gas above Well, the gas cap IS 6 years old, but the ball-checks were moving freely. The bike did not boil over, however it did appear to be running hot, which would be expected since I was running mostly 1st gear at about 10 mph with minimal air flow. My thoughts were that it may possibly be a plugged or stuck radiator cap. The hot, expanded coolant could not flow to the overflow, pressurizing itself. This would cause it to heat more and reduce cooling efficiency even further. I could not obviously check the radiator cap trailside as I don't like being scalded. I will check the cap tomorrow during the daylight, as well as checking my water pump, and changing the coolant. There was no steam, or the telltale stink of burning coolant in the exhaust indicating that I had blown a gasket so that is a plus. What do you folks think? Stuck radiator cap, stuck gas cap, with the combination of slow speeds and reduced airflow and all the above? Is there anyway to check the gascap and radiator caps for proper function? Thanks for the help.