Bob,
Those of us with classic coaches (read OLD) deal with this all the time. I will bet you that some of the rubber in the fuel system is shot. Actually, two things, that is a sucker bet and it is probably all shot. It goes bad just like tires. It will age out no matter what you do.
What to do about it?? Only one thing will be successful.
Take it apart and replace all the rubber with new. Those of us with classic coaches have all had to do this. Some of us more than one because the first only lasted 20 year and so I got to do it all again. This time I was sure to use alcohol tolerant materials.
Matt