Topic: Gas tank builds pressure (solved: had to drill gas gap)

[fmctm1sw]

As I prepare for the shakedown run to DMV on my 650, I notice the tank is building up pressure when the cap is on.  I have a NOS cap from a member here.  I dug around and found this thread:  http://forums.sohc4.net/index.php?topic=57700.0 that describes the vent passage as "next to those tabs."  I don't understand where that is.  I do have a small hole out towards the end of the cap.  I blew compressed air through it, no change...  Any ideas?

[Old Scrambler]

Clean the vent.......pipe-cleaner and gas......Check your lid gasket.......it may be too wide and is blocking vent when closed..........and don't park in the sun

[fmctm1sw]

    I dug up my old gas cap, thought I had thrown it away.  Notice the difference?  My old one has a vent hole in the center of the cap and the NOS one doesn't 

[fmctm1sw]

Oh well, solved.... sort of.  I tried to drill out that spot on the new cap hoping it was just capped and still had a passage underneath.  Nope, I snapped two drill bits attempting to drill it out at two different spots.  So the seal will come off and go on the old cap 

[fmctm1sw]

Well, I took a short break and got the bit out of it.  I used what was left of the bit and got through the cap.  Blew it off with compressed air and it vents fine now.  Since I already put the other cap on, I'll just sit this on the shelf until I need it.  That was an odd episode...   

[Magilla]

Are you building pressure or building vacuum?  There should be nothing more than atmospheric pressure in your tank at any time.  If your building vacuum it is the result of your cap not venting.  I've had that issue with a few bikes in the past.  For some reason it happened in high altitudes for my FXR.

My recommendation is to replace your cap.  Drilling it can allow trapped filings to get into your fuel system.  Bad things happen when pieces of metal make it into your fueling system.