Negative Pressure Vac in Tank - MVAgusta.net
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post #1 of 14 (permalink) Old 06-08-2019, 08:29 PM Thread Starter
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Negative Pressure Vac in Tank

Hi, Folks
Just replaced my warranty tank on a 2013 Brutale (2012 markings on the gas cap) with the US Evap Canister routed like the attached image. I'll probably pull the evap can at some point. Reassembled properly and started the bike with a small amount of gas which ran great at idle, while I tested for leaks, etc. Shut down and removed the cap and heard a negative vacuum. Closed cap and repeated, same thing. Left bike with cap closed and once again a bit of neg vac. Checked my plumbing and I can suck air up through the canister (can't blow because it is 1-way) from the tank (which does not taste good) and blow air from the other venting tube that exits the pump. Took off the tank cap and removed the strange red thing in the other picture -- parts fell out and I am not sure I assembled properly. There is a spring pushing a small metal diaphraghm with a small hole, a ball bearing and a rubber diaphragm,. My guess is that this is causing the problem but I can not find a parts diagram anywhere to let me know if I assembled it properly. The red thing is under the "M" looking thing in the other picture. Strange thing is I do not recall hearing the vacuum sound before the tank swap, and wondering if moving the evap canister or fuel pump around could cause this problem. Any help is greatly appreciated.
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post #2 of 14 (permalink) Old 06-09-2019, 08:08 AM
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Good morning. Just a curiosity question: As it is a warranty replacement, why didn't the dealer do the work?

As for the issue, air must flow into the tank to replace the volume of fuel that is removed during operation. You can actually collapse your new tank if that isn't;'t happening.

The device where the pieces fell out is likely a ball check device that allows air into your tank. I do not have one to look at, so I am surmising here.

It needs to be assembled in a way that allows air into the tank as vacuum builds (or pressure falls). I would assume there is a seating surface you can see and the assembly should be something like: AIR>SEATING SURFACE>BALL>SPRING>TANK internals.

Perhaps you could take it apart and post some detailed pictures of what is there as this is just a guess from the description.

On another, more humorous note: Vacuum is the absence of any material in a space. It is represented as a negative pressure. If you say you have a "negative vacuum" you are describing a positive pressure. (Double-negative) I don;t believe that to be your intent.

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post #3 of 14 (permalink) Old 06-09-2019, 08:32 AM Thread Starter
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Thanks. I will take a pic today. The shop is an hour away and they would need it for 2-days. I had no ride home or back.
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post #4 of 14 (permalink) Old 06-09-2019, 09:21 AM Thread Starter
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here are the pics. And yes, I meant to say "negative pressure" or "vacuum" but clearly that did not work out. I am 99.8% sure that this is right. No logical other orientation. I think this might have preceeded the tank warranty -- tank had a crack on one of the seams.
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post #5 of 14 (permalink) Old 06-09-2019, 09:30 AM
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My opinion......

The black piece is correct.

The rubber o-ring is the seat for the ball. The ball sits on the o-ring. The metal plate with the detent sits on the ball...detent toward the ball. The plate prevents the ball from entering the spring. The spring sits on the plate.

That assembly then installs to whatever receives it.

That is a spring ball check that lets air into the tank as fuel depletes.

There must be passages in that device for water to drain and fuel overflow.

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post #6 of 14 (permalink) Old 06-09-2019, 09:36 AM
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It would appear that MV has replaced the vent check valve that used to be part of the cap with this device mounted to the tank itself....

Do your self a favor, toss the spring and ball....of course, fuel could then leak from the cap in the event of a tip-over.

Go ahead and toss the evap cannister (actually only required in the state of California....all MVs in the USA are built to meet California emissions regulations). It is pretty straight forward.

As for the vent....you need to visualize the air flow path into the tank by way of that check ball. Air must be able to enter (the ball must overcome the spring when required). Air must also escape the tank...but it will be routed down the appropriate hose into the canister.

Good luck.

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post #7 of 14 (permalink) Old 06-09-2019, 09:41 AM
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It looks to me like MV has incorporated that assembly into the Fuel Cap assembly of ne MVs.

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post #8 of 14 (permalink) Old 06-09-2019, 10:00 AM
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Quote:
Originally Posted by silentservice703 View Post
It looks to me like MV has incorporated that assembly into the Fuel Cap assembly of new MVs.
It is part of the cap on all the older MVs (and most other bikes).... Haven't seen it mounted to the tank before (and not on any other bikes I'm familiar with).

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post #9 of 14 (permalink) Old 06-09-2019, 10:20 AM
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Quote:
Originally Posted by esq'z me View Post
It is part of the cap on all the older MVs (and most other bikes).... Haven't seen it mounted to the tank before (and not on any other bikes I'm familiar with).

What you are seeing, I believe, is the lower plate of the fuel cap assembly.....judging from the mounting screws.

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post #10 of 14 (permalink) Old 06-09-2019, 10:57 AM Thread Starter
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Thanks.
Looks like my logic is flawed. I think somehow it might have been assembled improperly because I heard the ball bearing bouncing around before opening that part. I truly appreciate your knowledge. Thanks
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