So how does the gas cap vent to air?

[Mandres]

Did anybody ever figure this out?  I've searched and read pages and pages but all I can find is a lot of speculation.  How does the gas cap vent to relieve the vaccuum in the tank?  I'm getting ready to seal my tank and I want to make sure I don't accidently seal up any hidden passages.

Thx

-M

[Jake D]

I want to know, too.  This is where Kerry comes in handy.  He explained this to me real good once.  He had a picture with a red circle on it but I forgot what the answer was.  I miss Kerry. 

[V8Pinto]

I JUST went through this this weekend for my fuel flow rate testing...

I completely disassembled the gas cap and figured it out.  The cap has a port from the inside of the tank to the atmosphere and it IS easily plugged.  It is sealed through a rubber gasket.  If you've ever taken apart a Holley 4bbl carb, the layout is similar to a metering block.  anyway....

The gas tank vent is THROUGH THE CAP.  That tube that drains from under the cas lid to down by the swingarm is NOT the gas tank vent, it is an overflow drain.  I found that my gas cap vent was clogged...  You have to take it apart and blow out the couple of ports in there and reassemble.  I did not take pictures but you'll figure it out.  Watch out not to tear the elastomer that seals the cap to the tank.  It stays with the lower portion of the gas cap when disassembled.  Also, watch out for falling parts...there are about 7 little springs and a ball bearing that like to take off and be free when you pull it apart.

It's not as bad as it sounds and was worth the half hour or so to figure it out...

[3imo]

The gas tank vent is THROUGH THE CAP.  That tube that drains from under the cas lid to down by the swingarm is NOT the gas tank vent, it is an overflow drain. 

I was the idiot that posted that.     sorry. that's what you get from thinking out loud.

[My Name Is Dave]

What exactly are you trying to figure out? Are you trying to determine where the gas cap vent holes are, or how they work in the whole scheme of the fuel system?

[Mandres]

I JUST went through this this weekend for my fuel flow rate testing...

I completely disassembled the gas cap and figured it out.  The cap has a port from the inside of the tank to the atmosphere and it IS easily plugged.  It is sealed through a rubber gasket.  If you've ever taken apart a Holley 4bbl carb, the layout is similar to a metering block.  anyway....

The gas tank vent is THROUGH THE CAP.  That tube that drains from under the cas lid to down by the swingarm is NOT the gas tank vent, it is an overflow drain.  I found that my gas cap vent was clogged...  You have to take it apart and blow out the couple of ports in there and reassemble.  I did not take pictures but you'll figure it out.  Watch out not to tear the elastomer that seals the cap to the tank.  It stays with the lower portion of the gas cap when disassembled.  Also, watch out for falling parts...there are about 7 little springs and a ball bearing that like to take off and be free when you pull it apart.

It's not as bad as it sounds and was worth the half hour or so to figure it out...

Any chance you could post step-by-step directions?  I actually destroyed the cap that came with my bike trying to take it apart (the lock was seized).  I have a replacement now, and I don't want it to suffer the same fate. 

-M

[Jake D]

Thanks for that info V8pinto.  It is worth it.  My gas cap sucks donkey balls. 

See Jake D's "GS left me stranded" thread.