Stupid ? regarding negative pressure on gascap

Apparently this is my first post. I have been lurking forever and even joined a while back but I don't seem to have posted once. So.... I am having negative pressure upon removal of the gas cap. And I mean sometimes it is pretty severe when it is only 1/4 left. I honestly only recall this occurring for the last year, maybe a year and a half. I have had it I think for 6 years. (it's a 2009 WR250X) It is not positive pressure build up, it is a vacuum. Clogged elsewhere or simply the cap is clogged. Isn't there a vent/breather hole in there?

Has anyone had this issue, did you fix it or is this common and no biggie?

Many thanks because now I am paranoid.

Stock gas tank? No, that is not normal, in a stock California gas tank the venting is through the charcoal canister, so something is being blocked in that line.

johnkol wrote:

Stock gas tank? No, that is not normal, in a stock California gas tank the venting is through the charcoal canister, so something is being blocked in that line.

I could have sworn that the hoses and canister were gone/tidied up but looking at the bike, the hose is right there. ugh. Now I have to check the over everything, starting pulling parts.

Msxxfast wrote:

I could have sworn that the hoses and canister were gone/tidied up but looking at the bike, the hose is right there.  ugh.  Now I have to check the over everything, starting pulling parts.

You mean the hose from the tank? Where does it terminate?

Easy test without taking parts off: remove gas cap and blow into that hose to gauge whether there is an obstruction. If you feel no obstruction, reconnect the hose and move to the next connector performing the same test, etc. until you find the obstruction.