Vortex gas cap

[Briggs]

I recently installed a Vortex cap for my GS. It installs easy and looks great. One problem... fuel starvation.  It seams to build up a vacuum in the tank as the gas drains out.  I know the cap was actually for a GSXR600 and I am wondering if there is something diferent about those tanks that allow them to breath. Anyone know? Dose anyone know anything about these? Any help would be awesome!

[weaselnoze]

idk much about these but does the new cap have a breather tube attactched to it? is it unobstructed?

[Briggs]

Well.. I just got in from the garage. It appears to have some sort of mechanizim for breathing. It dosn't have a tube attached but it does have a small hole with a very small bearing to block flow in the wrong direction. (hard to explain) It isn't easy but I can blow through it. So now I am really confused.

[weaselnoze]

its like a check valve then.  does the flow go into the tank?  so it can pull air into the tank to replace the fuel

[Jake D]

There is a drain tube that is for gas over flow or water.  The cap actually just vents through the top.

I've tried to figure out how to cure this same problem.  I may try to sand or score the rubber seal that goes around the cap.  This could actually be an awful idea, but if it is, I've got a spare cap!

[dgyver]

This is a common problem with Vortex gas caps. The spring is too strong and does not allow the tank to vent properly. An easy fix though.

Take apart the check valve by removing the allen screws and install a lighter spring. Cutting down the stock spring works too.

[Briggs]

My cap has two small bearings in it. One opens when there is a negative pressure in the tank. One opens when there is excess positive pressure in the tank.

The one that opens when there is positive pressure (pressure from empty tanks and a rise in temp.) has a spring. The pressure in the tank must overcome the pressure of the spring in order to "blow off".

The other uses gravity to seal the bearing against the bearing seat. The negative pressure or vacuum (When gas is flowing into the carbs.) in the tank must overcome the pressure that gravity puts on the very small bearing not a spring.

My solution was to spray carb cleaner through the oriface, then oil the oriface and repeat about five times. I bought the cap used on eBay and I think my problem was simply a matter of it being dirty. After cleaning it I went for a 45 min. ride with no problems.

At least I learned how the Vortex tank caps vent...