Vented or non-vented gas cap?

[ezridermn]

I have a 1982 Honda CB750c Custom. I want to modify my gas tank to use a spinner gas cap. There are two versions of the gas cap available. One is vented and one is non-vented. Which one should I use?

As always, thanks for the help!

 

[joevirus563]

I would take the vented... more air in tank = less restriction to carbs... just my 2 cent

 

[two-smoker]

If you don't use a vented cap you'll get vacuum inside the tank and eventually starve for gas. Unless you add anexternal vent to the tank.

 

[ezridermn]

I get the vacuum thing. Actually had a problem with a tank not venting several years ago. Question that then comes to mind is why do non-vented gas caps even exist?

 

[two-smoker]

You ever see the tubes on motocross bikes coming from the gas tank? That's an external vent. Some manufacturers use those on street bikes, whence the non-vented caps.

 

[VonYinzer]

All gas tanks are vented in some way.

 

[HerrDeacon]

Like Von said, all tanks are vented. A lot of the modern tanks have a tube within the tank, going from the top of the tank and exiting near the bottom of the tank. That's why there are vented and non-vented caps, depends on how the tank itself is setup.

 

[iagsxr]

Question that then comes to mind is why do non-vented gas caps even exist?

Twin tank Harleys use one vented one non-vented cap. Don't know why.

Modern bikes esp those with f.i. don't vent to the atmosphere directly. The vent goes to the airbox or somesuch. It's an emissions thing.