help with aftermarket engineering a gas cap vent tube ...

[timdhawk]

My gas tank has a recessed custom welded in "vented" pop-up gas tank cap that screws on/off. The tank is a cb750F model tank that had the stock emissions/vent port blocked off. The issue at hand is - come to find out - these pop-up caps are notorious for leaking when the tank gest hot and builds pressure. Gas leaks out thru the "venting" function of the cap and runs down the side of the tank.
My question: in simple terms, can I drill a hole thru the top of the cap and run a vent hose to help with the pressure build up and subsequent leakage issues? (the tube would be sealed at the cap) Anybody see any issues with doing this?

thanx

 

[timdhawk]

nuthin'...? nobody...?

 

[Sonreir]

I think you might be having other problems. There shouldn't be pressure build up in your tank because the excess pressure should be released by draining fuel into your carbs while the bike is running.

You can drill the cap, though. I did the same thing in my 360. Make sure you add a one-way check-valve to keep the fuel in the tank, though (not pictured).

 

[rockcitycafe]

you can do that, I know what you're talking about, the problem is that those caps are designed for tanks with evap systems, which vent at a very low to no pressure, so the check valve in the cap shouldn't ever function unless the evap system is blocked. the issue is that the pressure required to operate the cap check valve, either vacuum or positive, is too high, so when it pops, it's got some head behind it and can let out gas too