Isn't there a second skinny tube parallel to the filler tube that connects to the filler tube near the gas cap? I thought that was a vent line to prevent fuel being pushed up the filler tube. Maybe the vent line is plugged up?
Both of my 60's would make continuous gurling noises from the fuel tank in warm weather. I went as far as replacing the charcol canister on one of them hoping to solve the problem but it didn't help.
My 80 has developed the stinky fuel smell of a saturated charcol canister. I need to look into replacing it. On a recent camping trip after parking the the truck, I noticed the fuel smell and decided to just vent the tank pressure and get the smell done with quickly. I loosened the cap and the pressure surged out of the tank but didn't stop as I expected. It kept going, I waited maybe 30 seconds and the flow continued so I resealed the cap and found something else to do. Maybe it was the combo of the altitude, the heat and the ethanol content that made the system evaporate so rapidly.
'03 KTM 450EXC
"If you know what you're doing, then you aren't learning anything." - A. Lincoln