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Old 11-07-2010, 06:33 AM   #1
loph917 OP
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gas tank vacuum

i'm wondering if i have a blocked vent tube somewhere...

when i fill up with gas while i'm opening the gas tank i can hear what seems like a very good vacuum being released...i don't seem to remember this behavior before.

my question is; am i suffering from a blocked vent tube or other form of blocked venting somewhere? can other f8 owners (us) chime in and let me know if i'm going crazy (ok, we already know that answer)?

thanks.
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Old 11-07-2010, 07:21 AM   #2
Mr B
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If you are hearing a vacuum sucking sound when you open be warned you are not venting the fuel tank. Here in California we have these nifty little charcole filters, I dont understand them completely but believe they are suppose to eliminate teh fuel vapors when you park the bike in the garage.
Anyway last summer I was riding and it was extemely hot, we were climbing up out of the Kings River Canyon, about 3000 feet. As I was climbing up the bike stutterd and stopped running. I stopped and restarted no problem and then about 1/4 mile later, same thing.
I opened the fuel tank to ensure that there was fuel still on board, I was not out of gas but did hear that sucking sound. This repeated itself once more at which I opened the fuel filler cap, wedged some paper under and taped the cap down. this let the tank vent I we climbed and no more stalling.
The next morning, we camped that night up fairly high, +/- 7000 feet, I closed the fuel tank and went home, I did not want to break down on a trail miles from home, so I slabbed it home, no problem. When i got home I inspected the fuel vent line that travels aft of the fuel tank and ties into the charcol canister. I did not see anything but I did relocat the vent line in an attempt to ensure that it would not be blocked when I carry a load on the back of the bike.
I guess what I am saying is be careful if you pinch that vent line you will can create a vacuum in the fuel tank, and eventually the fuel pump will not be able to overcome this vacuum.
Hope this helps, sorry so wordy...
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Old 11-07-2010, 07:39 AM   #3
johnparjr
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Mine has a little suction when I open it and I have never had a problem. There is an older post on this somewhere and most people had some suction If I remember correctly.
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Old 11-08-2010, 05:47 AM   #4
JRWooden
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Not sure which bike you have, but the charcoal canister on the F880GS/F650GS twins can cause this issue.
There is a recall active on it.
If you have one of the twins you may have a plugged canister.

If you have a different bike it still could be same/similar problem

Search for "charcoal canister" there was a lot of chatter on this about 6 months ago but it has died down now since the recall and etc...
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Old 11-08-2010, 06:18 AM   #5
ebrabaek
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As stated above..... there is a recall on the Carbon canister. That said..... If you want to investigate it your self...... Take off the yellow plastic on the top of the tank..... There will be a little 10mm or so od hose running from the top of the tanks backwards then under the seat, and down to the CC. Right before said hose runs under the seat, you will find a little tubular shaped valve. Make sure the arrow on it points towards the tank....NOT away from it. I have heard of some claiming theirs was installed incorrect. When you remove the hose from the tank.... try to apply suction to the tank end.... It should flow freely... If not... Said hose is the key to you problem. If the CC is plugged.....or the valve is not working the vacuum is not alleviated in the tank.


Erling
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Old 11-08-2010, 09:59 AM   #6
Dansrc51
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or just remove the charcol filter and eliminate that and a few other problems all together...
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Old 11-08-2010, 10:47 AM   #7
EnderTheX
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Quote:
Originally Posted by Dansrc51
or just remove the charcol filter and eliminate that and a few other problems all together...

That's what I did. Screw the environment, at least I'm not driving a giant truck like everyone else in Texas...
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Old 11-08-2010, 11:04 AM   #8
Dansrc51
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Quote:
Originally Posted by EnderTheX
That's what I did. Screw the environment, at least I'm not driving a giant truck like everyone else in Texas...
I'd be willing to bet the difference in emmissions is minimal, by comparison. I mean between with canister and w/o.
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Old 11-08-2010, 04:50 PM   #9
ebrabaek
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Quote:
Originally Posted by Dansrc51
or just remove the charcol filter and eliminate that and a few other problems all together...
Yes .....as I did as well...... But you still need to check the valve...thus removing the plastic..... some have been reported to be installed the wrong way......

Erling
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Old 11-08-2010, 09:46 PM   #10
JRWooden
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Quote:
Originally Posted by ebrabaek
As stated above..... there is a recall on the Carbon canister. That said..... If you want to investigate it your self...... Take off the yellow plastic on the top of the tank..... There will be a little 10mm or so od hose running from the top of the tanks backwards then under the seat, and down to the CC. Right before said hose runs under the seat, you will find a little tubular shaped valve. Make sure the arrow on it points towards the tank....NOT away from it. I have heard of some claiming theirs was installed incorrect. When you remove the hose from the tank.... try to apply suction to the tank end.... It should flow freely... If not... Said hose is the key to you problem. If the CC is plugged.....or the valve is not working the vacuum is not alleviated in the tank.


Erling
Erling:
I should allow air to move freely INto the tank and also allow air to come out of the tank after it reaches some modest pressure of ... several PSI?

Is that correct?

Thanks!
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Old 11-08-2010, 10:32 PM   #11
johnparjr
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So what is the vacuum effect doing to my gas tank?
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Old 11-08-2010, 10:42 PM   #12
EnderTheX
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Quote:
Originally Posted by johnparjr
So what is the vacuum effect doing to my gas tank?
It's robbing you of your mojo man! Dude...







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Old 11-09-2010, 06:49 AM   #13
ebrabaek
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Quote:
Originally Posted by JRWooden
Erling:
I should allow air to move freely INto the tank and also allow air to come out of the tank after it reaches some modest pressure of ... several PSI?

Is that correct?

Thanks!
Yeppers JR.... your correct. I cant speak of the correct pressure..... But when I applied 5psi against the arrow (away from the tank flow) my valve began to slowly vent. If you applied any suction on the discharge side of the valve...( away from the tank)...it instantaneously opened up and flow free. That had me concerned..... because when the .....purge valve i think it`s called.....opened up during engine operation....a vacuum vas applied from the manifolds....through the CC....up through the said valve....and it opened without any resistance. I wondered if that was the way it was meant to be......then decided that it was not detrimental, since the motor was not running while parked....and pressure was still being vented....so off went the CC.....no issues since. I am not an advocate of just yanking stuff off the bike.....specially emission stuff..... But when BMW cant figure this one out....even with the y hose installed..... Then it gotta go. I think that next time I`m in there..... I`l just remove the valve itself.....and everything will flow free.....in either direction..... I think there is a tip over valve in the tank before the nipple where the hose is attached.....that prevent any fluid to escape if the bike takes a nap......so the little check valve is not needed..... IMHO... but as usual ...perhaps I`m missing something.......
Joel should bee here shortly to correct me......


Erling
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Old 11-09-2010, 06:53 AM   #14
ebrabaek
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Quote:
Originally Posted by johnparjr
So what is the vacuum effect doing to my gas tank?
I a perfect world....there should be no suction when opening the tank......Thus no vacuum present...... A little is propperly ok..... But if you have a swoooosh..... there is something going on.......and you are making the Fuel pump work overtime.....and it has enough issues with the ethanol plugging the artery`s......... You should have a look.....

Erling
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Old 11-09-2010, 08:28 AM   #15
loph917 OP
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thanks for all the replies everyone; i haven't had a chance to go out and check things over yet (since posting the original query) but its good to know that this is just another hiccup in the life of an f800gs and seems to be relatively easily solved.

i am beginning to think that all the quirks the f800gs has exhibited has worked to help us better understand how all the various systems on the machine actually work. if it ran perfect all the time would we be as educated about it?
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