Quote:
Originally Posted by spdbrake
Typically the fuel caps are vented and it sounds like your is not.
Another issue if the tank vent line (that usually runs from the top corner of the tank to the side of the fill line) has a low spot (right after it leaves the tank, typically look will like a J vs the required L shape) it will cause the fuel to start backing up the fill pipe as temperature increases. If can be exasperated even more if the return fuel line dumps into the fill line as well.
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The screw-in fuel cap I'm using is vented, but it has a one way valve that lets air pass in but not out of the fuel tank. I'm sure this one way vent is for pollution control as otherwise the fuel vapors would be constantly vented to the atmosphere.
I did check the vent line on the gas tank to ensure it was clear when I first noticed this fuel tank pressurization issue. It is. I do have the EFI return line T'd into the vent line. This is probably not ideal but CRL didn't design this tank for EFI so it doesn't have a dedicated port for the fuel return. I can say that using the vent port for fuel return hasn't seemed to be an issue for the 20+ years that it's been used this way.