Help: Fuel leak when weather gets warm

[frogseatflies]

When the weather is cool, I have no fuel leak.  When it gets hot, fuel starts leaking at the underside of the gas tank where it junctions with the Auto Fuel Cock Assembly.   I checked the hose clamp around the Auto Fuel Cock Assembly with a screwdriver and it seemed tight.    I tightened it more and it seemed to not affect things.     I took the tank off and took a good look and the O-ring inside looks in perfect shape.    So I'm not really sure what's going on.   

Of course, one thought is that maybe the hose clamp isn't really as tight tight tight as it should be.

I find it interesting that it only leaks when it gets hotter.   So the vapors (or whatever you call it) build up enough pressure that it forces a leak.     That makes me think there's not something here to regulate the gas vapor pressure?... or if there is something for the vapor pressure regulation, that it is clogged or not doing its job properly.

Any ideas?

[Stig / Major Tom]

On a hot day, when you open the gas cap.....do you hear air pressure escaping?
If so, might indeed be a clogged tank vent.....the tiny metal pipe itself or.rubber hose attached to it.
If no pressure building up in tank , sounds like a hose or seam leak. Not over filled is it?
Keep us posted please.
Stig

[frogseatflies]

Stig, thanks for your response.

It was cooler this morning and I put in just a little bit of gas until I filled up the tank about half-way.  It got hotter later on.  So just now, I went outside to my scooter and I smell gas.  So I tested your theory.  I unscrewed the gas cap and definitely heard air pressure escaping... almost like the tank was saying "ooh god, thank you for releasing this pressure."    So, thank you for your idea.    It must be a clogged vent.    I know the tiny little pipe coming up didn't seem to be clogged.  So I wonder if it's one of the hoses downline.

[BettinANDlosing]

Stig, thanks for your response.

It was cooler this morning and I put in just a little bit of gas until I filled up the tank about half-way.  It got hotter later on.  So just now, I went outside to my scooter and I smell gas.  So I tested your theory.  I unscrewed the gas cap and definitely heard air pressure escaping... almost like the tank was saying "ooh god, thank you for releasing this pressure."    So, thank you for your idea.    It must be a clogged vent.    I know the tiny little pipe coming up didn't seem to be clogged.  So I wonder if it's one of the hoses downline.

The factory system allows NO vapor to vent into atmosphere, because EPA laws. Take a small drill bit, very small like .5mm and drill into the plastic gas cap. Whala no more vent problems.

[0BARK4322]

Yep, that did sound like a pressure build-up

[frogseatflies]

PROBLEM/SOLUTION:   I Replaced the the fuel petcock assembly... and there we go!   Solved.   (The original was leaking.)

[CROSSBOLT]

It will stick eventually. Then vent the gas cap.

Karl

[eamartin]

What's deal with these Kymco diaphram fuel valves?  Are they junk or what?  Mine would not close completely when the engine was shut off, so I threw on a cheap Chinese eBay valve I got from my brother.  So far, so good.  Is there a quality replacement available?  Of course, there could be a piece of debris stuck in there preventing the valve from closing, but these things are not made for disassembly/inspection.

[CROSSBOLT]

Sticking OPEN is no problem unles you are under a tipped over bike. Stuck SHUT causes engine problems.

Karl

[eamartin]

Sticking OPEN is no problem unles you are under a tipped over bike. Stuck SHUT causes engine problems.

Karl

Or...The float valve is not sealing properly.  I'll need to address this since I did not bench test it before re-installing the carb.  Shame on me.