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Discussion Starter #1
I'm looking for a replacement fuel tank breather check valve for a carbie 900ss. Mine is completely corroded. Does anyone know where I can get either the OEM replacement or aftermarket replacement that works? I have one from some other machinery, but this one is pretty chunky at almost an inch in diameter. I'd want something a bit smaller like the original. Appreciate your suggestions!
 

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Depends on where you route the hose, (My 95 dives down the steering stem hole so it still is inline), but those $10 anodized ones for dirt bikes at CycleGear work fine. Just put a longer hose on and put the vent breather piece at the end instead of hanging out on top of the tank with two hoses. Miy 91 routed is under the fairing and zip tied to the frame out of sight unless I put the CR fairing on.
 

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Discussion Starter #4
Thanks for the response!
Yeah, $88 is a bit much!! I think I'll try a dirt bike one. Thanks again!
 

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Discussion Starter #5
I have an additional, related question - so the one that I put on from the other machinery (it's from a pile of parts for things like industrial air compressors and water cooler and stuff like that) works well as a one-way check valve, but I found what could be an unintended consequence, maybe? The way I understand is that the breather valve should let the air in the tank to replace the fuel that is being sent to the carbs, right? What's happening is that now the one-way check valve works, every time I open the filler cap, it blows out puff of (petrol smelling) air, meaning that it appears to build a positive pressure inside the tank (from the heat?). Is this normal? The filler cap obviously is not vented, is there supposed to be the secondary vent? I'm still very new to 900SS, so I'm very curious to learn. By the way, I had an early GSX-R 750, which had a breather hose, which had no check valve, and I don't remember that it leaked fuel.
 

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The cap usually does have a vent into the chamber under the cap. from there you have one or two ways for it to exit.
#1 the cap drain that should be the recessed hole at about the 7-o'clock position if you are setting on the bike.
#2 later cap flanges with California emissions there will be a rubber bumper looking thing at six o'clock. this is actually a passageway from the cap to the charcoal canister. if either of these holes/vents are plugged they cannot de-pressurize the tank. It is not un common to have a tank vent plug either internally from rust or externally from insects or simply pinched off.
 

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Discussion Starter #7
The cap usually does have a vent into the chamber under the cap. from there you have one or two ways for it to exit.
#1 the cap drain that should be the recessed hole at about the 7-o'clock position if you are setting on the bike.
#2 later cap flanges with California emissions there will be a rubber bumper looking thing at six o'clock. this is actually a passageway from the cap to the charcoal canister. if either of these holes/vents are plugged they cannot de-pressurize the tank. It is not un common to have a tank vent plug either internally from rust or externally from insects or simply pinched off.
The overflow, or the cap drain is working fine. There's the recessed hole there (the 7 o'clock hole that you are talking about, I think), it's actually not a hole. I looked at it when it was off the fuel tank, but there's no hole that goes through. Is that supposed to be open? I guess I can drill it out.

 

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Thats the same as my 91 900SS the hole at the rear is not a thru hole
 

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Do you experience positive pressure inside? Today, I'm riding without the check valve.
The check valve is to prevent anything from getting into the tank, humidity, water, ants,... it should also do a pretty good job of slowing down a gas leak through it if you suddenly find yourself rubber side up.
 

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Discussion Starter #12
On non California emission bikes the rear hole is not drilled. you can see the hole in the bottom of the tank latch that lines up with the emission hole it is were there. As is the cap should vent into the cap area and vent through the drain. is the vent hole plugged?
An interesting info about the CA emission stuff. Because the fuel filler cap mechanism was seized, I had to disassemble the cap, and noticed that there was an elaborate passage for something, but now I see that it’s for the vented gas. Anyway, so the drain is working fine, meaning the positive pressure buildup is not venting passed the sealing part of the cap. I poked the little hole on the cap’s latch cover, and it’s not blocked. I may have to take it apart again to study the filler cap one more time to see how it works, it might be more complicated than I thought.
 

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Discussion Starter #14 (Edited)
Sounds like you are on the right path, I see it often with aftermarket caps that have no vent system.
I took the filler cap apart. The small hole at the bottom of the latch, there’s a lot of space inside there that houses the latch, and the bottom of the lock. There’s a plate, then there’s the spring loaded filler cap seal. There’s a little rectangular chamber that has two small holes that leads into the chamber that’s shaped like two circles in shape of ‘8’, from which there’s a pathway defined by the cap and gasket to the little hole that lines up with CA emission related hole that ducvet mentioned. Here’s the weird thing - mine had a rubber piece in the shape of ‘8’ that fits in that chamber that blocks the flow of the vented air. I removed the rubber piece, so that vented pressure can leave through the cap area. I’ll take a ride tomorrow to see if that’s what, but I’m pretty sure that’s what the problem has been. I should have taken some pictures.
 

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Discussion Starter #16
I don't think it is venting at the highest point in the tank now,...
Erm, yeah? See, the one-way check valve was shot, so I got new one, right? It does let air in to the tank, not out, right?, so to replace the fuel spent with air, basically. But since I replace the check valve, I noticed that the tank holds positive pressure inside, probably from heat, since while it lets air in, it’s not letting air out. The logic suggests that there’s no other place to let the pressure out, so I think it’s a reasonable conclusion, at least it seems to me.
 

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Here’s the weird thing - mine had a rubber piece in the shape of ‘8’ that fits in that chamber that blocks the flow of the vented air. I removed the rubber piece, so that vented pressure can leave through the cap area. I’ll take a ride tomorrow to see if that’s what, but I’m pretty sure that’s what the problem has been. I should have taken some pictures.
I have two that I took apart. One from my 996 and one from my 900SS. They're identical. Right down to that orange rubber piece shaped like a number 8 as you referred to it.

As both mine are California compliant versions, I'm guessing yours, or at least your cap is also. There was a secondary hose that routed evaporative emissions back to the charcoal cannister. and a return hose that went back up front to the air box. Assuming your bike is a California spec bike anyway.

My guess is, that secondary hose is either blocked or the hose barb where it connected is now covered with a vacuum plug. I have an aftermarket cap on both now....but the 900SS is still immobile so I can't answer any question regarding if it works in relation to the tank vent though. ....sean
 
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