gas cap hissing at me!

[Guest]

my buddy Felix is a crazy Russian(not sure his english is good enough for him to make sense of this site) with a 79or 80 550l. This problem he has does not happen on initial startup, but when we are out riding, and the bike is nice and hot, when we stop for a break or whatever, when he re-starts the bike, a long and audible hiss is heard and the overpowering smell of gas arises. we found it is pressure coming out of the gas cap.
**What is causing this "back pressure" and what is the fix?**

[hikermikem]

The heat of the engine heats the fuel tank up, thus expanding the fuel within...

Take the fuel cap off & make sure the tank vent hole is clear - it's located on the side of the tank filler neck. Has the tank been sealed recently? Sometimes that hole gets filled with tank sealant.

The tank then vents through the filler cap keyway - clean that as well.

[loud et]

thanks , sounds right on, I will see how that works.