Pressurising fuel tank, normal?? - MVAgusta.net
 
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post #1 of 9 (permalink) Old 05-09-2016, 07:30 AM Thread Starter
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Pressurising fuel tank, normal??

I have noticed recently that I am getting wheezing/groaning sounds from the fuel tank after I stop.

When I pop the fuel cap there is a definite release of pressure, I can't tell if it's negative or positive.

Is this normal?

My old ZX-6R used to do it fairly often and you could often hear it "moan".
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post #2 of 9 (permalink) Old 05-09-2016, 08:32 AM
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Mine certainly does it and always has. And mine is positive and continues to pressurise at a standstill with a hot engine - assuming the fuel heating up and evaporating a bit.

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post #3 of 9 (permalink) Old 05-09-2016, 08:43 AM
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Your gas cap vent is working, but may be restricted somewhere. Check the small hoses that come out the bottom of your tank for kinks.

(I presume the 3 cylinder bikes have a water and vent drain hose like the 4 cylinder bikes do).

The flip side of this is when the hose is blocke or pinched completely off...the the fuel pup pulls a vacuum strong enough to collapse a metal tank and deform a plastic one.

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post #4 of 9 (permalink) Old 05-09-2016, 10:50 AM
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That's a fair point - actually noticed while I had the belly panels off recently that the hole cut for the water and vent drain pipes is a bit tight for both. It takes a good amount of force to get the vent pipe through with the drain pipe in the hole. I imagine the vent pipe could be nipped up and causing a restriction, albeit not tight enough to resist much pressure.

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post #5 of 9 (permalink) Old 05-10-2016, 01:40 AM
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This happens regularly, especially on hot days where the sun heats the tank. I have solved the problem but can't remember what I did. Pretty sure it was make sure the hoses aren't pinched which involved tank removal. I would be surprised if the pinching is related to the hose going through the fairing
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post #6 of 9 (permalink) Old 05-10-2016, 03:12 AM Thread Starter
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Hmmm.. cheers guys. I will have check this, don't fancy taking the tank off, but I'll trace it as far up as I can.

I'll also give the dealer a shout and get them to check it at next service. The bike is due it's annual service although I still have at least 2000 miles left, so was just waiting on the nice (as nice as it an get in the UK) weather to do the 100 mile trip up to them.
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post #7 of 9 (permalink) Old 05-10-2016, 06:32 AM
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Quote:
Originally Posted by emmevi125s View Post
I would be surprised if the pinching is related to the hose going through the fairing
Just been out to check and with the F3, you can handily check all the way from the tank connections (by feel through the back of the frame and sight with a torch from the right of the bike) and visually check the pipe as it goes down the right hand side of the bike. In my case, definitely no crimps, pinches or twists right until it goes through the belly panel, where it's crushed by the larger drain tube that also goes through the same hole.

The hose is definitely deformed at that point - not enough to completely blocked, but I can imagine it quite happily making the moaning noise I hear in the same way an old fashioned fart cushion works

Wildfire - it's simplicity itself to check your hose - not a job for the dealer - you don't need to take the tank off, or move anything.

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post #8 of 9 (permalink) Old 05-10-2016, 10:52 AM Thread Starter
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Brilliant, thanks Shug. I'm away with work at the moment, otherwise would pop out and have look.
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post #9 of 9 (permalink) Old 05-10-2016, 10:00 PM
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Thumbs up ?

It can also be defective assembly of the cap, all the little check valves and flappers

my Aprilia RSVR cap was wrong and leaked too



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