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Discussion Starter · #1 · (Edited)
I'm trying to understand what a parts supplier / manufacture has told me, about their fuel caps. My question basically was: If I do a test as if bike is crashed, and turn the tank up-side down, I expect it not to leak (specifically fuel cap/ from under it).

The guy replied to me: (from a big brand producer)

"The only place the cap will leak is through the venting pipe.
Without the venting pipe the tank would vacuum and the engine would be starved of fuel."

So I'm irritated with myself, I don't understand how the venting pipe works, what he wrote, and what does that imply.

The venting pipe is the 'hole' in the tank, for the air to get in. So is he saying, not matter what, if you turn the tank on the side or upside down, it will leak through the venting hole?

The venting pipe is at the bottom of the R1's tank, no (fuel tank breather hose)? So if fuel is coming out, it will be dripping from that pipe.

What does this venting pipe has to do with the cap, what am I missing?

Please someone explain to me how it works. I don't want to get a wrong idea that a leaking fuel tank is Ok .. even if bike is on it's side. :eek5:

(all I know is, when I turn the tank over with the stock Yamaha OEM cap nothing freaking leaks from the tank, period)


:dunno
 

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where its Ok for fuel tank to leak..

This is on my 2002
Ok you have 2 nipples on the bottom of the tank 1 vent 1 overflow on the inside of the tank are 2 metal lines that go from the nipples to the top of the tank to the cap.
Auto part Wheel Rim Automotive wheel system Automotive tire
that's the overflow.. Actually a series of holes all the way around the cap
Auto part Brake Disc brake Vehicle brake Wheel
thats the vent and the rubber seals to the bottom of the cap small hole in next photo
Auto part Wheel Automotive wheel system Brake Clutch


Here is one of the metal lines
Blue Light Purple Violet Electric blue

Should only leak on the overflow side
Hope that explains it


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Discussion Starter · #6 ·
This is on my 2002
Should only leak on the overflow side
Hope that explains it

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Hey Zac, thanks for writing detailed with pics explanation.

But but.. I still need to clarify something.

So does the air get into the tank through the small venting hole, which joints into the cap (the pink rubber seal on which the cap sits, with the small hole) ?
If I understand it, then the air gets from the bottom nipple/hose, through the pipe inside the tank, then into the cap (where pink seal is), and through the cap into the tank? And this what guarantees the fuel will flow?
(but if there is a hole in the cap for the air, won't it leak too ... ?)

When you say it should leak on the overflow side, do you mean that it should only & only leak when petrol comes out from the top of the tank (out of the opening where you put petrol in), and spills around the cap base?
Or do you mean that, if you turn the tank upside down, with cap closed, then the petrol will still come out from underneath the closed cap, and then it should ideally get through the overflow holes around the cap base, and down the overflow pipe... ? (mm, but how, if the tank is on the side, or upside down ...).
 

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Nothing should leak from the cap, the cap you bought is junk if it leaks.
However a cap also need a vent hole on it to allow the air coming up the vent tube to bypass the seal on the cap and let the air in the tank to replace the fuel, they normally use a little bearing style non return valve in them.
This is why a cap that is made to look like an $90.00 dollar cap but only costs $20.00 will often cause problems, The tank will pressure lock and stop the flow of fuel.
Yours is either bad design, bad seal or crap vent valve.
 

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where its Ok for fuel tank to leak..

Hey Zac, thanks for writing detailed with pics explanation.



But but.. I still need to clarify something.



So does the air get into the tank through the small venting hole, which joints into the cap (the pink rubber seal on which the cap sits, with the small hole) ?

If I understand it, then the air gets from the bottom nipple/hose, through the pipe inside the tank, then into the cap (where pink seal is), and through the cap into the tank? And this what guarantees the fuel will flow?

(but if there is a hole in the cap for the air, won't it leak too ... ?)



When you say it should leak on the overflow side, do you mean that it should only & only leak when petrol comes out from the top of the tank (out of the opening where you put petrol in), and spills around the cap base?

Or do you mean that, if you turn the tank upside down, with cap closed, then the petrol will still come out from underneath the closed cap, and then it should ideally get through the overflow holes around the cap base, and down the overflow pipe... ? (mm, but how, if the tank is on the side, or upside down ...).

Only leak on the overflow side if overfilled... If the tanks upside down it shouldn't leak at all...
Now the vent works because there is a check ball inside the cap that blocks the passage in case it's overturned as Redgecko said
To clarify vent air comes in the nipple through the tube up the rubber hole into small hole in cap then enters the tank through this gap when tanks closed Auto part
that seal on the spring keeps fuel from getting to the overflow area from splash and roll over when caps closed cap being closed opens gap and the air vents into tank (stock cap)


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Discussion Starter · #9 ·
Nothing should leak from the cap, the cap you bought is junk if it leaks.
However a cap also need a vent hole on it to allow the air coming up the vent tube to bypass the seal on the cap and let the air in the tank to replace the fuel, they normally use a little bearing style non return valve in them.
This is why a cap that is made to look like an $90.00 dollar cap but only costs $20.00 will often cause problems, The tank will pressure lock and stop the flow of fuel.
Yours is either bad design, bad seal or crap vent valve.
Hi Redgecko !

Please check my thread here, last post:
http://www.r1-forum.com/forums/showthread.php?p=7235977#post7235977

See cheap Ebay vs Harris. Not much difference I see.. Also, both will leak , as far as I understand. Just that Harris has hose to direct leak to overflow ( I think...)

Check it out ! comment if can
 

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Discussion Starter · #10 ·
Only leak on the overflow side if overfilled... If the tanks upside down it shouldn't leak at all...
Now the vent works because there is a check ball inside the cap that blocks the passage in case it's overturned as Redgecko said
To clarify vent air comes in the nipple through the tube up the rubber hole into small hole in cap then enters the tank through this gap when tanks closed View attachment 720945 that seal on the spring keeps fuel from getting to the overflow area from splash and roll over when caps closed cap being closed opens gap and the air vents into tank (stock cap)


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Oh Zac Agee, thanks man, for taking time & pics to explain . (well a bit late with my thanks :tongue:)

I see original Yamaha cap is a very well safe design. I can't quite say the same about the aftermarket stuff. See my pics comparing ebay vs Harris there, in my thread.

http://www.r1-forum.com/forums/showthread.php?p=7235977#post7235977

I see both are about same ...
 

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Kind of off topic, but what is the purpose of the quick release fuel cap? I mean the key for the stock unit is less than two feet away in the ignition. The only thing I can think of is that you can fuel the bike while it is running, or is it just it looks cool?
 

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Kind of off topic, but what is the purpose of the quick release fuel cap? I mean the key for the stock unit is less than two feet away in the ignition. The only thing I can think of is that you can fuel the bike while it is running, or is it just it looks cool?
It's better than stock. Trust me. Try it.



 

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Discussion Starter · #13 · (Edited)
Kind of off topic, but what is the purpose of the quick release fuel cap? I mean the key for the stock unit is less than two feet away in the ignition. The only thing I can think of is that you can fuel the bike while it is running, or is it just it looks cool?
Hey YZF-Rich,

You don't have any keys on race /track bikes .People remove all locks.

Well in my case I will have key for ignition. But I did get a second, damaged tank off ebay, to use just for those track weekends and some club racing.

Hmm, but now I'm thinking, i can get an old stock fuel cap, brake the lock somehow so i can open it with screwdriver, and use that.
(I rather have that, than any cool looking aftermarket cap, or any ~200usd caps)
 
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