Gas Cap K1100RS 1994, not venting

[Lssartin]

My bike has did this since I bought it.  The gas cap is not venting, bike makes a big sucking sound when you open the cap after riding.  This causes a negative pressure in the tank and unless I open the cap and keep it open it will not start.  I want to know how to fix this and confirm others have had the issue.  I have confirmed the vent hose to the cap is free and clear, can only be the gas cap unless the tank vents elsewhere.  The part under the cap appears to be the culprit, it does not allow venting.  My problem is the gas cap cost  $250 and they do not sale the part under the cap individually. Lot of money when everything I have said is my own opinion and deduced after a couple years of guessing; not actually sure the cap is the issue but certain my bike has negative pressure build up in the gas tank, harder I ride the worse it is and this causes the bike to not start unless I vent the tank.  If I vent the tank and close it, it immediately builds negative pressure and must be vented again to start.  Any replies are appreciated guys.

[Inge K.]

FYI: when choosing K11 on Maxbmw........only part# xxx 403 is shown.

[Scott_]

Also sounds as if the "vapor recovery" vent inside the tank could be partly plugged as well.
A lot of riders/owners have removed the vac line that connected this tank vent to the engine block, and replaced it with the "air accumulator cup". In essence venting the tank to atmosphere.
This eliminates overfilled gas from being sucked into the crankcase and diluting the oil, and also eliminates the "vacuum" condition inside the gas tank.
One side effect of this is you can/will occasionally smell fuel fumes on nice warm days.

[Lssartin]

Also sounds as if the "vapor recovery" vent inside the tank could be partly plugged as well.
A lot of riders/owners have removed the vac line that connected this tank vent to the engine block, and replaced it with the "air accumulator cup". In essence venting the tank to atmosphere.
This eliminates overfilled gas from being sucked into the crankcase and diluting the oil, and also eliminates the "vacuum" condition inside the gas tank.
One side effect of this is you can/will occasionally smell fuel fumes on nice warm days.

I do not understand "air accumulator cop". Really need a solution, please keep posting anything that will assist. Thanks to all.

[Lssartin]

I understand air accumulator cup now and think this will most likely fix the issue.  California emissions bike. Thanks

[Niemand]

I could be way off here, as I haven't had the problem luckily, but I recall reading about people accidentally putting one of the seals in the cap gasket setup in the wrong orientation, thus blocking a vent of some sort.  Perhaps someone with more experience could expand on that, but thought I would throw it out in case it is a possibility.

My bike is a CA bike as well, and removing the one way valve and switching to the "cup" was a simple process.  I've been meaning to post some photos I took during that process for a while now, as it is often mentioned but seldom with pics.  I'm pretty good at procrastinating when I get around to it.

[frankenduck]

All 86+ USA bikes have the stuff to be CA compatible.  It increases production and other costs to make one model for CA and one model for other states.  Some manufacturers do make CA-specific models of their products but that's not the case with Ks.

[Niemand]

All 86+ USA bikes have the stuff to be CA compatible.

Learn't something today, and it's barely after lunch.  Good to know for future reference.  I just assumed mine had all that chit because it was originally sold in Santa Rosa, CA.

[Scott_]

I could be way off here, as I haven't had the problem luckily, but I recall reading about people accidentally putting one of the seals in the cap gasket setup in the wrong orientation, thus blocking a vent of some sort.  Perhaps someone with more experience could expand on that, but thought I would throw it out in case it is a possibility.

If you look at your gas tank filler from the position of sitting on the bike, on the left side there is a hole for the purpose of draining accumulated rain water around the gas cap. Ideally when the bike is on the side stand leaning left.....
Problems can be encountered if you put the cap gasket on with the wrong orientation and cover the hole. Or if you turn the cap any direction other than having the hinge face the seat.

[WayneDW]

Mine did that because the hoses at the bottom right of the tank were kinked.  I 2nd the suggestion to install the air accumulation cup.  It made the removal and re-installation of the tank much easier and no longer a worry about the kinked hose.  And it wasn't much money either!

[Niemand]

... rain water...

Thanks, _

That was it...and as warned, way off mark here.