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Old 11-09-2010, 08:09 AM   #16
JRWooden
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Quote:
Originally Posted by ebrabaek
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
Thanks ...
When you look at the parts diagram there seems to be more valves there than might be "required' ... a tip-over valve (yah good) and then at least two more valves....

sigh................

Work gets in the way again of me learning important stuff....
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Old 11-09-2010, 10:19 AM   #17
itsatdm
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There are 2 switches. 1 on the tank and 1 on the throtle body. Even if the charcoal filter is removed there could be some suction in the tank as it takes 1.5 psi to activate the tank switch.

Here is Joel's explanation of the system: http://www.advrider.com/forums/showt...420546&page=29 post 426
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Old 11-09-2010, 05:59 PM   #18
JoelWisman
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Quote:
Originally Posted by loph917
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.
Am I correct that your not experiencing any starting or running issues?

When I run into this question at my dealership, the first thing I do is to T in a pressure / vacuum gauge, just past the tip over valve on the fuel tank and ride the bike. Nearly always nothing is wrong amd pressure and vacuum remain bellow 1 psi.

Next both right after a ride, and after the bike has set, both cooling and warming, I hold a thin piece of tensile next to the filler cap. Almost always what the customer perceives as a strong vacuum is infact pressure. I've begun taking bets on this and have earned 40 us dollars so far.

Up to 4.5 psi of pressure, and 1.5 psi of vacuum below ambient is normal.

There is a sure sign of the fuel tank holding excessive vacuum, the fuel cap will not spring open and must be pulled on to break the vacuum.

In the rare instance that vacuum is excessive, the problem has always been a blocked canister vent tube or a stuck roll over valve.

The same additives that protect fuel injectors and fuel pumps will keep the roll over valve from sticking. Chevron techron concentrate fuel system cleaner, or, BMW fuel system cleaner + with techron.

The canister drain valve can be prevented from blocking by removing it occasionally and blowing it out.

How often it needs to be blown out varies, but it will never block unless the bike is run in deep mud or a spider builds a web in it.

It also helps to route the canister drain line so that it terminates high and near the side stand, protected by the side stand frame. Cutting the end of the vent line at a 45 degree angle also helps.

I don't know what is happening with your specific bike, but statistically in my personal experience, nothing is usually wrong, the owner just noticed the sound when enviornmental and other variables were right for the first time.

The gold standard of tests is to have a runnability problem that disappears when the fuel cap is left open.

This test carries risk that fire proof BMW techs are untrained to deal with :)
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Old 11-11-2010, 01:44 PM   #19
johnparjr
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Mine is in the shop as I type this I decided better safe than sorry hopefully I won't be waiting long.
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Old 11-11-2010, 05:26 PM   #20
johnparjr
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1 1/2 later I had a pinched hose and a bad canister will have to go back next week as they didn't have the canister in stock I asked if this could have caused any damage to the tank and I got no response.
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Old 11-12-2010, 10:17 AM   #21
JRWooden
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Quote:
Originally Posted by JoelWisman
The gold standard of tests is to have a runnability problem that disappears when the fuel cap is left open.

This test carries risk that fire proof BMW techs are untrained to deal with :)
from past experience I know I'm not fireproof at all..........
I have tossed one of those little red plastic straws from the WD-40 cans in my tool roll. I figure if ever suspect a vacuum I can close the tank lid with the straw stuck in there and it will allow enough air in to keep the vacuum away (maybe) and prevent me from having to re-learn that I'm not fireproof!
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