Glad to hear I'm not the only one with this problem! Everybody told me to try the race gas solution. Other than being a total PITA, it didn't work for me. I went to Vickery Yamaha on Parker Road and bought some 110 Octane. Since the road tax isn't paid with their racing fuel (they are a motorcycle dealer) you'll have to pump it into a gas can. No fuel boiling with the race gas, but the boiling problem returned at a 50/50 ratio. Seemed like a dead end to me. Besides, since everything boils at lower temps at altitude, where can you buy race gas in the mountains? I can still boil fuel in the summer, too.
A guy I know buys his fuel in Elizabeth, CO. Elizabeth is supposedly outside the emmisions area. Seems like a waste to use half a tank of fuel to get to a gas station that sells ethanol-free fuel.
What I've had "success" with is an electric fuel pump. I drive with one hand on the steering wheel, one hand on the shifter and one hand on the fuel pump switch. It can get very tricky!
When the fuel starts to boil, I shut off the fuel pump for about 10 seconds. Sometimes it's 10 seconds on, 10 seconds off, but I can keep it running. When I was getting a dyno-tune done the carburetor looked like Old Faithful, shooting a geyser of fuel out of the primary vent tube about 4-5 inches high! I try to stay out of stop-and-go situations. I also try to shut the fuel pump off about 20 seconds before I shut the engine down to keep flooding on restart to a minimum.
Having to do all of this is a pain, but it keeps the wife from wanting to take the car anywhere by herself.
Al Bockman