Author Topic: Fuel tank vacuum  (Read 572 times)

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Offline Tjnoma99

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Fuel tank vacuum
« on: January 01, 2018, 10:31:37 pm »
Yesterday i went on a ride. Nothing long, maybe 50 miles around town. I parked my bike in my driveway and went it. When i came out to put my bike in the garage, i heard a humming. Initially I thought it was my fuel pump still running. I stood the bike off the kickstand and the noise got louder. I quickly started the bike, because i was afraid if it was the pump, it would kill the battery or flood the engine. The noise stopped and i put my bike away. Today i went for a longer ride ( roughly 250 miles). When i stopped for gas, the fuel cap had a suction behind it. Made a sucking sound when i opened it. After i filled up, I parked it next to a buddys bike and it made that same noise. Its coming from the tank. Anyone know what it could be? Maybe a pinched vent line? Its a 13 with 18k miles.
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Offline jwh20

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Re: Fuel tank vacuum
« Reply #1 on: January 01, 2018, 11:14:46 pm »
There is a vent in the cap that should equalize pressure given enough time.  It's a really small passage that's designed to let air in and out but not allow fuel to exit.  It can get clogged so if you think it's not working right you can take the cap apart and clean it out.
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Offline Tjnoma99

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Re: Fuel tank vacuum
« Reply #2 on: January 01, 2018, 11:49:08 pm »
Ok cool. What should i clean it with?
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Offline Old Man on a Connie

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Re: Fuel tank vacuum
« Reply #3 on: January 02, 2018, 12:30:54 am »
Mine whistles Dixie at me  ;) I wouldn't worry about it unless you see a performance change, The vent  IMHO is set at X PSI, X HG's. There will always be residual. My .02
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Offline gpd323

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Re: Fuel tank vacuum
« Reply #4 on: January 02, 2018, 12:32:42 am »
Mine always makes a slight sucking sound when I open the cap to fill up, same on the ZX14. And in the summer it makes a high pitched sound from the cap when I come home and turn it off and the hot engine below heats up the fuel in the tank and its venting. I call it normal.
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Offline Tjnoma99

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Re: Fuel tank vacuum
« Reply #5 on: January 02, 2018, 12:43:03 am »
So its' the call of the connie' then :))
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Offline Jerdurr

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Re: Fuel tank vacuum
« Reply #6 on: January 02, 2018, 03:17:58 am »
Mine always makes a slight sucking sound when I open the cap to fill up, same on the ZX14. And in the summer it makes a high pitched sound from the cap when I come home and turn it off and the hot engine below heats up the fuel in the tank and its venting. I call it normal.
same for me.
Best,

JD

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Offline Steve in Sunny Fla

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Re: Fuel tank vacuum
« Reply #7 on: January 04, 2018, 11:29:56 am »
I've wondered about this. In a gravity fed system, the vacuum will stall the fuel flow. with a pump, I would assume the vacuum will build to a pretty high point if not vented. I wonder if this could affect fuel flow. sorry, no answers on this one.  :o  Steve
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Offline touring03

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Re: Fuel tank vacuum
« Reply #8 on: January 04, 2018, 02:14:07 pm »
I know many say to leave it and not worry about it, that it's normal, but it's not normal, if it was normal the bike would have been making that sound from day one, my bike didn't start making that sucking sound until the 6th season on the road.  If it's a fairly easy fix then my choice would be to fix it.  Now that I know it's an easy fix it'll be top of my list before I hit the road this spring.

PG

Offline BDF

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Re: Fuel tank vacuum
« Reply #9 on: January 04, 2018, 05:48:34 pm »
A little bit of vacuum in the tank is normal, and the venting system in the fuel fill cap often makes a small but high pitched 'squeal' after the bike is parked; this is often known and the Kawasaki 'squeak'. If you can open the fuel fill cap, there is not much vacuum in the tank; if there was a significant amount, you would simply not be able to open the cap because outside air pressure would 'clamp' it closed. A modest resistance to opening the fuel tank immediately after running the bike is fairly normal.

On fuel injected vehicles, there is always a danger of a fuel tank vent failing. Because the fuel pumps for F.I. vehicles are high pressure units, they will also pull a very high vacuum, more than sufficient to literally crush the tank from an internal vacuum and normal outside air pressure. But this is generally a problem on Italian bikes rather than Japanese bikes. Do a quick Google search and you will find a LOT of European bikes with crushed fuel tanks- it is honestly quite disconcerting to see (and I am sure even more disconcerting to own such a bike  :-\

Brian


Yesterday i went on a ride. Nothing long, maybe 50 miles around town. I parked my bike in my driveway and went it. When i came out to put my bike in the garage, i heard a humming. Initially I thought it was my fuel pump still running. I stood the bike off the kickstand and the noise got louder. I quickly started the bike, because i was afraid if it was the pump, it would kill the battery or flood the engine. The noise stopped and i put my bike away. Today i went for a longer ride ( roughly 250 miles). When i stopped for gas, the fuel cap had a suction behind it. Made a sucking sound when i opened it. After i filled up, I parked it next to a buddys bike and it made that same noise. Its coming from the tank. Anyone know what it could be? Maybe a pinched vent line? Its a 13 with 18k miles.
KiPass keeping you up at night? Has the low fuel warning burned your retinas? Find peace, harmony and the answer to these problems. www.incontrolne.com

Offline jacksdad

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Re: Fuel tank vacuum
« Reply #10 on: January 04, 2018, 06:33:39 pm »
My Isuzu Trooper 3.0 4x4 had a problem with fuel supply, when low on diesel, it would misfire. When I removed the filler cap, the rush of air going into the tank was shocking! Not just a 'normal' sort of hiss, a LOT of air went in...so I started leaving the cap a little loose, its under a locking flap and 3 feet above the tank so no problems. I've modified it a lot, its lifted 7" and I think the breather tube that runs alongside the filler neck, has been squashed. I've now drilled a pinhole through the filler cap, and its perfect again  ;D

Offline RWulf

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Re: Fuel tank vacuum
« Reply #11 on: January 04, 2018, 09:30:24 pm »
Is the squeal sound due to a vacuum in the tank or vapor pressure?
Does the C-14 use a fuel return line from the fuel pump? I don't
have a 14 so I ask. On our C-10's, I believe the rubber flapper valves
in the gas cap are hardening over time due to our friend alcohol. As
gas is differant all over the country the change in the flexibility of
the rubber happens at differant rates, there are some that squeal
and there are some that don't.
Educated me on this.

Offline JTX

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Re: Fuel tank vacuum
« Reply #12 on: January 04, 2018, 09:47:53 pm »
It's a normal sound.  Its vented through the canister mounted in the top right fairing.

Offline BDF

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Re: Fuel tank vacuum
« Reply #13 on: January 04, 2018, 11:53:24 pm »
Well, I can only pass on what I know so take it for what it is worth....

The C-14's tank is vented through the fuel cap, for both pressure and vacuum. Pressure would occur if you fueled a bike with cold fuel (as from underground tanks) on a hot day and then parked the bike; the fuel would expand and the cap vents the excess pressure.

It also vents vacuum, or more accurately, lets air into the tank as the gasoline vacuum goes down. For example: you start to ride the bike with a full tank of fuel and as the fuel is used up, either something needs to fill the volume that the gasoline <used> to occupy, or the tank will develop a vacuum. If the tank were sealed and ridden long enough, the fuel pump has sufficient pressure to cause the tank to actually collapse due to the vacuum created inside, with atmospheric pressure outside.

The fuel cap has a couple of pretty involved vents in it, including a labrynth seal. It is actually surprisingly complex and looks like this: (fob shown for size comparison)

 

The labrynth and labrynth seal:



This is the actual vent housing:



And the vent itself, which consists of a plunger (the brass, pointed part) and an O-ring:



As I said before, they vent slowly and so often give the 'Kawasaki whine'. It is pretty amusing at a Kawasaki dealership on a busy day 'cause they kind of compete with each other. :-) The noise is generated by the air escaping past the spring loaded valve (shown above) and makes a noise similar to a balloon being vented by squeezing the neck of the balloon.  Mine was replaced under warranty because it was not venting pressure correctly, when the bike was fairly new back in '07 or '08 at the latest. I am not aware of a tank collapse happening on any Japanese bikes but the vacuum vent (the one that lets air into the tank to replace the volume that  was displaced by fuel as the tank is emptied) but it is / was a problem on European bikes, mostly Italian bike or so it seems.

Brian

Is the squeal sound due to a vacuum in the tank or vapor pressure?
Does the C-14 use a fuel return line from the fuel pump? I don't
have a 14 so I ask. On our C-10's, I believe the rubber flapper valves
in the gas cap are hardening over time due to our friend alcohol. As
gas is differant all over the country the change in the flexibility of
the rubber happens at differant rates, there are some that squeal
and there are some that don't.
Educated me on this.
KiPass keeping you up at night? Has the low fuel warning burned your retinas? Find peace, harmony and the answer to these problems. www.incontrolne.com

Offline Jerdurr

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Re: Fuel tank vacuum
« Reply #14 on: January 05, 2018, 01:56:55 pm »
When I park my bike after filling up the tank with a warm engine on a hot day, i can hear the "Kawasaki Whine" clear as day. I look at my bike and say: "how dare you pass gas in my presence!?" and laugh to myself like a complete dork.

I call them Kawi farts.
Best,

JD

--Harley Davidson is king when it comes to turning gas into smoke, without the outcome of power--

Offline RWulf

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Re: Fuel tank vacuum
« Reply #15 on: January 05, 2018, 02:43:30 pm »
Hay Thank You!   Good pic too.

Offline Daytona_Mike

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Re: Fuel tank vacuum
« Reply #16 on: January 05, 2018, 07:45:52 pm »
no motorcycle fuel tanks crushed from not venting but i did find this one
https://www.youtube.com/watch?v=2WJVHtF8GwI
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Offline BDF

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Re: Fuel tank vacuum
« Reply #17 on: January 05, 2018, 08:55:43 pm »
Yeah, it does not seem like it would amount to anything but 14.7 PSI, normal air pressure at sea level, can be quite powerful. We do not normally experience its effects because most things are either vented to allow that same pressure inside so the pressure is balanced (like our motorcycle fuel tanks) or strong enough to withstand the pressure, such as vacuum flasks and so on. But as the fuel pumps on fuel injected vehicles produce 40+ PSI, they are capable of also creating a very strong vacuum by pumping fuel out if there is no way for air to enter the tank and balance the pressure. As I said, it does seem to be found more often on Italian bikes than motorcycles in general but that is just my observation, not real data or even evidence.









The other way works well too; every once in a while there would be a motorcycle tank, hugely distorted and miss- shapen, hanging on a dealer's wall. All the ones I have seen are the result of using compressed air inside the tank to 'pop out' a dent without damaging the paint, etc. And while it usually does remove the dent, it also puffs up the tank like a Ball Park Frank if the user is lucky; they burst and spread shrapnel around if the user is not so lucky.

Brian

no motorcycle fuel tanks crushed from not venting but i did find this one
https://www.youtube.com/watch?v=2WJVHtF8GwI

KiPass keeping you up at night? Has the low fuel warning burned your retinas? Find peace, harmony and the answer to these problems. www.incontrolne.com