Author Topic: Fuel tank pressurisation  (Read 5670 times)

Offline Bikebear

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Fuel tank pressurisation
« on: August 29, 2012, 08:39:31 PM »
Just wondering if when you open the fuel cap on your ST it whooshes like it's pressurised. The cap has a vent hose attached but it doesn't seem to release the pressure. Anyone got any thoughts.
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Online Brock

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Re: Fuel tank pressurisation
« Reply #1 on: August 29, 2012, 08:46:46 PM »
They all do it,
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Offline saaz

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Re: Fuel tank pressurisation
« Reply #2 on: August 29, 2012, 09:25:13 PM »
They do all whoosh, but it is a known issue where the cap does not allow air into the tank once it runs lower. (Having pressure in the tank is normal due to controlling petrol vapour emissions - the whoosh should be release pressure, not letting air in due to a vacuum)  One way to tell is if the bike runs better after releasing the cap, and runs worse with it on going for a while before releasing it.  The vacuum builds up counteracts the pump trying to get petrol out.  You can take the cap apart and make sure it is working ok - I have a diagram somewhere about how it works if you need it.  Mine makes lots of noises it hot weather as the pressure in the tank is vented.
John
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Offline royst1100

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Re: Fuel tank pressurisation
« Reply #3 on: August 30, 2012, 07:30:51 AM »
about 2 weeks ago i heard a buzzing sound after a short ride on hot day that could be heard several meters away . took time to track down but ended up a pressurised fuel tank. been meaning to quiry this as ive never had that happen before.
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Offline bluehonda

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Re: Fuel tank pressurisation
« Reply #4 on: August 30, 2012, 07:39:04 AM »
It's not so obvious with a full tank as the air space above the fuel is smaller.  Less air to heat up, expand and escape.
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Offline saaz

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Re: Fuel tank pressurisation
« Reply #5 on: August 30, 2012, 09:38:25 AM »
And here is a diagram on how it works. The ST13 probably has a more car like system with a closed loop.
John
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terrydj

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Re: Fuel tank pressurisation
« Reply #6 on: August 30, 2012, 02:27:04 PM »
"learning everyday"
I always thought that noise was my radiator cap letting off a bit of steam that's why???? well on my bike anyway, the noise stops and starts :think1
 

Offline saaz

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Re: Fuel tank pressurisation
« Reply #7 on: August 30, 2012, 04:04:51 PM »
The noise does stop and start, as the bikes residual heat expands the petrol/air in the fuel tank. Sounds a bit like whale noises on a hot day, as the pressure is relived first time, then a while later when it builds up.
John
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Offline STeveo

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Re: Fuel tank pressurisation
« Reply #8 on: August 30, 2012, 04:42:40 PM »
I thought it was my 1100 humming to itself because it had enjoyed the ride too.   :whistle

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terrydj

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Re: Fuel tank pressurisation
« Reply #9 on: August 30, 2012, 05:05:13 PM »
The noise does stop and start, as the bikes residual heat expands the petrol/air in the fuel tank. Sounds a bit like whale noises on a hot day, as the pressure is relived first time, then a while later when it builds up.
Thanks mate :thumbsup was actually thinking about checking the coolant in me radiator cause its been happening for a few years now
 

Offline tj189

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Re: Fuel tank pressurisation
« Reply #10 on: August 30, 2012, 05:55:07 PM »
I've lost a few decibels in the upper range so I have never heard it >:()
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Offline Oddjob

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Re: Fuel tank pressurisation
« Reply #11 on: August 30, 2012, 08:23:58 PM »
Exactly the same thing happens with mine, I like to think of it as a sigh of satisfaction after a ride.
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