fuel tank vent

[lil'doozer]

Why is my right fuel tank pressurizing on its own. When I fill the tank and keep the filler cap tight, the tank will pressurize and dump fuel. I have tried parking the plane in flight position but it still pressurizes. I am keeping the fuel level between 1"- 2" below totally full. My wing was a quick buld. Has the vent been installed incorrectly? What's up?

 

[AltonD]

Make sure the vent line is not blocked.

 

[Squeak]

Maybe a leak inside the tank

My left tank built up pressure. Did some air pressure test and found I had a leak inside the tank at the vent line fitting. Removed the tank inspection plate at the wing root and found (inside the tank) the flare had cracked at the fitting. What would happen was with the fuel above the fitting the line would fill up with fuel and the tank built up pressure than burp fuel out on the floor.
Squeak

 

[longranger]

Why is my right fuel tank pressurizing on its own. When I fill the tank and keep the filler cap tight, the tank will pressurize and dump fuel. I have tried parking the plane in flight position but it still pressurizes. I am keeping the fuel level between 1"- 2" below totally full. My wing was a quick buld. Has the vent been installed incorrectly? What's up?

I'm assuming it's dumping out the vent? If the fuel is 1" to 2" below full, then the open end of the vent line should be above the fuel. You should be able to check it with a mirror through the fill port. If that end is OK, you might want to check the security of the interior B-nut on the inboard fitting.