Fuel Flow Problem

So here's a weird one: I leave my bike in storage for a lil' while, take it out for a ride, and oddly enough, the fuel won't flow when I open the petcock. I usually have to pull off the fuel line from the petcock (while it's open), at which point the fuel spills onto the ground a bit. I VERY QUICKLY reconnect the line, and everything works great...at least until the next time I put the bike away.

Seems like some kind of back-pressure holding the fuel. Any thoughts as to what the problem could be?

non venting gas cap?

That would be my guess too...POPS

If the fuel flows when you remove the fuel line and do not vent by loosening the cap the problem is not a non-venting cap. It would be more likely to suspect a sticking needle valve at the float. Do you have to blow the line? Is there fuel present as soon as you pull the line off the carb or after a moment? How long is the bike stored before you experience this problem?
Tom

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If you did not drain the carb and gas line before storage, I bet the whole innards of the carb have gotten varnished up.
I never recommend storing a gas tank empty though, it invites rust.
Before storage, disconnect the fuel line from the fuel valve and cap the ends of the line and valve barb off with rubber vacuume line caps, available at auto parts stores.

Now that it is too late for you, take apart your carb and clean it well with carb cleaner spray.
Wear a face shield or goggles, and if you get any on you, wash it off well, even if you think it evaporated away. It will leave residue on your skin.

Yeah, it still happens when I take the gas cap off, though I do keep it covered in duct tape so it doesn't stank up where I'm storing it (I take the tape off for a ride).

If the carb was really screwed up, why would it still work so well once I pull off the line for a couple seconds and then put it back on? Seems like a seized valve would stay seized?

The valve may not be seized, just sticking. My only assumption is there is varnish build up in the float needle seat, float needle itself, or the float arm pivot.
The only other thing I can reason it to be is the float bowl vent is blocked, which is highly unlikely.

If the floatbowl is full when you finished last time you rode it, then it should be pretty full when you come back to ride it. You won't see the fuel flowing until you use some of the fuel in the fuelbowl. That will unseat the needle valve and fuel will start flowing again. If the needle valve is getting stuck try STA-BIL fuel stabilizer. It should keep your gas and fuel system fresh.

Funny thing is that if I try to drive it a bit it'll cough and sputter like it has no gas, so I can only assume the float bowl is empty. That varnishing issue sounds alot more likely, so I'm gonna start there (though I was really hoping to avoid cracking open the carb). Probably this weekend or later, I'll post my results.

Thanks for the help, guys.