Ski Sits for 20 minutes then hard to start

I have a 2001 Yamaha XL800, It runs great with one exception. after riding approximately 20-30 minutes or longer, If I stop 20-30 minutes or longer, it will not just crank up and go. If Im lucky , I can feather the throttle and it will clear up and go. One dealer says its a vapor lock caused by heat escaping via the carburetor. Another dealer says its because the engine cools off so fast that I need to choke it when restarting it. Chocking doesn't solve the problem. Once it gets going again, it runs fine. What do you think.
Steven

Steven, It sounds like you have a bad needle and seat in the carburetor. When you sit for 30 minutes the seat leaks and can flood your engine and makes it hard to start.  Get a carburetor rebuild kit.