Aloha,
I just got one of the jp cycles gas caps on my 02 883 I love the look but I think the cap isnt vented i put it on and i believe its causing gas to come out of the overflow. says its vented in the description. I put the old cap back on leak stopped
anybody else have this problem??
Mahalo

 

I think the cap vent should only allow air in, to equalize pressure as you use fuel, so that should not make a difference to overflow. Now, if you filled your tank to the top, let it sit out in the hot sun, gas expands a lot, and I'd assume you'd get gas going into the overflow vent, on through the vapor valve, and on to be stored in the vapor can (until you start your engine, and it purges out). If you have no vapor can, it will push past the vapor valve and drain/vent to atmosphere. CA bikes have a vapor can, other states bikes don't. Not sure about HI. They all have vapor valves AFIK, if only to minimize evaporation.

Think of the cap as a one way valve in for air, and the vapor valve as a one way valve out for overflow and vapors, mostly vapors. but gas is possible.

I always fill just to the lower part of the filler bung, so there's plenty of room for expansion. Have not had a problem with my open overflow tube and dirtbike breather ever leaking gas. I eliminated my vapor can and vapor valve.

Might just be as simple as thermal expansion, not the cap. If your cap is not vented, and you have the vapor valve, you would experience fuel starvation due to vacuum inside the tank as it emptied, not leakage.

John

 

Look for the vent hole and see if it's plugged or even there at all.

 

I can't see how a cap would cause gas to come out the over flow

If it sealed air tight it would simply prevent air from coming in and cause a vacuum inside the tank causing the fuel to stop and therefore the bike quit running