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Offline flatfour

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Fuel tank venting
« on: August 10, 2015, 09:54:07 AM »
Whilst at the Kawasaki Dealer on Friday, I mentioned that there was usually a sucking noise when opening the fuel cap and a "whistling/ creaking" from the fuel tank area after using the bike.

They said that there is now a reed valve in the fuel venting system that causes the tank to vent only when pressure builds up and, as long as it makes these noises and there is sucking when the fuel cap is opened, it is operating as intended.

Offline Sir Rupert

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Re: Fuel tank venting
« Reply #1 on: November 03, 2018, 02:51:48 PM »
I have never heard any sucking noises on opening the tank on any bike ever....until this morning.
I opened the tank of my MkII Versys to fill up and got a big 'whoosh' as I did so.
I filled up with as much fuel as I could squeeze in and rode the one mile home from the petrol station. On reaching home, I opened the tank and was rewarded with a tiny squeak: the fuel level had dropped about half an inch in the neck of the tank.

So my question is, is it supposed to do that and if so, why have I never noticed it happen before? :187:
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Offline Crosshairs

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Re: Fuel tank venting
« Reply #2 on: November 03, 2018, 04:17:30 PM »
*Originally Posted by Sir Rupert [+]
I have never heard any sucking noises on opening the tank on any bike ever....until this morning.
I opened the tank of my MkII Versys to fill up and got a big 'whoosh' as I did so.
I filled up with as much fuel as I could squeeze in and rode the one mile home from the petrol station. On reaching home, I opened the tank and was rewarded with a tiny squeak: the fuel level had dropped about half an inch in the neck of the tank.

So my question is, is it supposed to do that and if so, why have I never noticed it happen before? :187:

It sounds to me like the vent tube is clogged.

Offline Sonny

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Re: Fuel tank venting
« Reply #3 on: November 03, 2018, 05:33:41 PM »
As I understand the evaporative emission control system, when the bike (or car) is shut off and  parked in the sun where heating inside the tank is producing positive pressure, fuel vapor from evaporation in the tank is sent overboard through a restrictive charcoal cannister which absorbs the vapor before air exits the tank vent hose. When the engine is running, fuel pulled into the engine produces a net vacuum in the tank due to the sealed gas cap and the restriction in the charcoal cannister. Now air flows backward into the tank, pulling the fuel absorbed by the charcoal back into the tank for burning.

The wheezing or whistling when you shut off the bike is air running back into the tank until the vacuum inside has settled down to ambient air pressure. Same with the whoosh when you open the gas cap. It is air flowing in to equalize the vacuum in the tank. In other words, there is no emission of fuel vapor into the atmosphere. Then while you pump gas, as we all know, you often get a face full of fuel vapor. The rubber bell around the end of the filler pump nozzle is supposed to suck up these vapors, but it only does so if the filler nozzle is driven all the way down on the flange around the fill hole, which on bikes it often isn't.

If someone knows more or knows different, please inform us.
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Online 100milesaway

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Re: Fuel tank venting
« Reply #4 on: November 03, 2018, 11:19:31 PM »
All the above mentioned noises and characteristics are perfectly normal.  :002:
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Offline Crosshairs

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Re: Fuel tank venting
« Reply #5 on: November 04, 2018, 12:50:58 AM »
*Originally Posted by 100milesaway [+]
All the above mentioned noises and characteristics are perfectly normal.  :002:

I dont get any of those noises or symptoms...but my bike does not have an evap system.

Offline Sir Rupert

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Re: Fuel tank venting
« Reply #6 on: November 27, 2018, 01:51:59 PM »
I used a 20ml plastic syringe filled with petrol to flush the area around the filler neck and also squirted some down a little vent hole in the cap and into a corresponding tube running into the tank. There has been no repeat of the problem since so it looks like Crosshairs was right when he said it sounded like a blockage.  :759:

Fingers crossed it doesn't happen again, ha ha.
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Offline SouthernCruizer

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Re: Fuel tank venting
« Reply #7 on: November 27, 2018, 07:23:43 PM »
Be aware that it is entirely possible to kink your vent tube when changing the oil, depending on how you move the vent tube while doing so. If you change oil and the gas cap is tough to open and has pressure, the tube is most likely kinked. Routing the line properly will fix the issue.
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Offline uralrob

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Re: Fuel tank venting
« Reply #8 on: November 28, 2018, 02:32:33 AM »


  All 8 Kawaskis that I have had, going back to the '80s, have whistled and wheezed through the cap vent as the fuel expands and contracts. As I putter around the shed happily achieving nothing I find it very soothing. In fact I some times chat back to them  :36: .

 However, for those who find it distracting a minor tuning may be in order  :2:.

 Rob.

Online 100milesaway

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Re: Fuel tank venting
« Reply #9 on: November 28, 2018, 09:11:42 AM »
*Originally Posted by uralrob [+]

  All 8 Kawaskis that I have had, going back to the '80s, have whistled and wheezed through the cap vent as the fuel expands and contracts. As I putter around the shed happily achieving nothing I find it very soothing. In fact I some times chat back to them  :36: .

 However, for those who find it distracting a minor tuning may be in order  :2:.

 Rob.
   So you chatter back to a noise Rob  :question::138: :5: :124: :goggle: :lostit: :758: :760:         :745: :745: :745:
If man evolved from monkeys, why are there still monkeys?

 



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