gas tank vacuum buildup

[Nserio2004@yahoo.com]

I have a 1996 BMW R1100RSL that fell over onto its right side when I neglected to put up the side stand while wheeling it onto my lift in preparation for replacing a leaking front master cylinder. Damage was minimal, the mechanism that raises and lowers the windshield broke but that was the extend of apparent damage. However, since that time the gas tank builds significant vacuum during operation which I cannot determine is a new or deteriorating condition. I have checked the vent lines and find that if I blow through the vent line not connected to the canister I can feel air pressure through the vent hole in the filler cap. If I blow through the vent line connected to the carbon canister with the gas cap open, I can see gas vapors exiting up through the filler. Any ideas or suggestions as to the problem and a remedy will be appreciated. Thank you

[mneblett]

Not completely clear on your comments --

It sounds like you blew through the filler rim rain drain hose, and it is clear.

It sounds like you removed the hose from the tank vent running into the canister, and blew back toward the tank, and found the tank clear.

If this is correct, I suspect that if you try to blow through the canister you will find it blocked, most likely from fuel that travelled to the canister during the tip-over.

If this is the case, two choices: replace the canister or perform a canister-ectomy. A fuel-wetted canister is generally a goner, as the fuel causes the activated charcoal to turn into an air-blocking slurry.

A canister-ectomy and proper re-routing of the hoses/blocking off of the intake hose will eliminate the potential for future canister problems.

[Nserio2004@yahoo.com]

Thanks for the input and advice. I suspected that it was a canister problem. My wifes' Ducati 620ie advises not to raise the tank when full as gas will flow into the carbon canister rendering it useless. Since the vacuum issue seemed to coincide with the tip over, it seemed to make sense that more than likely the canister was flooded. Thanks again for your help, Nick