Fuel overflow from fuel cap

[xzap042]

Hi, I have this weird issue of fuel overflow from filler cap after filling up fuel tank. Car is carb Cultus.
Normally I dont fill it till full but yesterday morning I filled it up till full, was not overfilled, stopped on auto. After filling up went to office. Car was parked outside under sun. When I came back in evening there was fuel overflow stains on paint. Basically fuel overflowed from cap. This has happened once before as well but at the time the tank was slightly less that full. I have checked breather pipe and its not clogged.

I'm going to change fuel cap as well but I want to know what could cause fuel to overflow from filler cap?

[hasan337]

i guess someone try to stole patrol from your car throgh suction pipe.

[Xulfiqar]

Your vent valve is stuck closed. Have mechanic check and clean/fix/replace it.

[xzap042]

Both breather hose and fuel vapor line are open when blowing into them. Should I check the other way as well?

It really pains me as this fuel overflow has caused yellow stains on clear coat and they're not coming out

[Xulfiqar]

You see that tiny box on the vapor line,

Thats clogged.

[xzap042]

That's the first thing I checked. Anyways, checked again today and it's open both ways. There's no structure or valve sort of thing inside it. It's just a simple box with two holes on each side. The hose that connects to it is also open when blowing into it and very slight resistance when vacuum is applied.

[Xulfiqar]

Check the valve in middle of the tank too.

[xzap042]

Right will drop the tank and check