Clogged gas tank vent, or ?

[inkblot]

Hi All,

 

I've been a bad owner, and let my 2004 V11 Sport sit for too long (again). After replacing the battery, and doing some cursory safety checks, I gave my bike a bath and went for a ride. Everything felt great

 

When I got back home, I was parked in the sun, and about two hours later I noticed a small puddle of fuel under the bike. The fuel was clearly dripping from the overflow tube, which made me think that it might be by design when the tank gets hot. I opened the tank cap and a big whoosh of hot air came out as the tank contracted a significant amount.

 

I thought maybe this was just an extreme heat thing (though it wasn't really that hot out, and I've never seen it before), and the tank pressurization (and thus fuel overflow) would stop once everything cooled off. So, back in to the garage, this time w a little cardboard underneath in case of any drips.

 

Later that evening, the cardboard was soaked in fuel. It was a warm night, but nothing out of the ordinary. At this point I figured I had a real problem- something is not letting the tank pressure escape- and I came here to search the boards for help. After reading a number of similar posts, I'm still a bit confused about how the tank vent system is supposed to work.

 

Here's what I did, with no luck: I unscrewed the associated hex screws and removed the gas cap assembly. It has a little black rubber nipple which sits in the corresponding hole in the rim around the filler opening. I blasted the whole cap assembly w compressed air, and it seems like air is flowing freely from the nipple to the little holes in the red plastic center part of the cap. This suggests to me that the pressure in the tank should escape through the little holes in the cap, to the nipple, then back down and out of wherever that hole in the rim leads.

 

I shot some compressed air directly into that hole in the filler rim (it's the one on the right, again where the nipple from the cap seats) and it sounded like the air was escaping, but I can't tell from where.

 

Also, I shot some air into the other hole in the rim, and the air escaped freely through the overflow tube and out the bottom of the bike. This was expected, as my puddles of fuel indicated there was no restriction here...

 

So, let me start with perhaps a really dumb question, at the heart of my confusion: How does the tank pressure build up to the point of forcing fuel out through the drain tube? I.e., why doesn't the air escape through that same path?

 

Second, assuming I still have a blockage somewhere, where might that be? And how does one clear it? The problem began only after I swapped the battery, washed the bike, and went on a ride. I'm thinking maybe some soapy/dirty water found its way into the wrong place and created the blockage (?).

 

Thanks in advance!

 

Jake

[Kiwi_Roy]

Perhaps the tube below the tank is pinched?

 

 

Sent from my shoe phone!

[czakky]

Do you still have the US emissions plumbing hooked up?

[inkblot]

@kiwi: It's possible, I'll take a closer look- but I doubt it, as air flows through just fine when I blast compressed air into the corresponding little hole in the filler rim.

 

@czakky: Yes, the bike is pretty much as new (only 1900 miles). I haven't (yet) messed with any of the emissions stuff.

[GuzziMoto]

There should be two different lines from the tank. One is the overflow, which is the one from the rim of the filler. The other is a vent and that one is inside the tank. With the cap closed it is the vent line that vents the tank to the atmosphere.

There was a one way valve in our V11's vent line from the factory, it can allow air in as fuel is used but doesn't allow air out. A common mod is to remove that one way valve.

[inkblot]

@GuzziMoto: Thanks for the detail. Yeah, I read about that in one of the other posts; it sounds like removing that one-way valve may be a fix, and it may be the fastest path to getting back on the road.

 

That said, how does it make any sense? Not that everything in the world needs to make sense to me in order to work

 

What I'm getting at is, if the vent from inside the tank is designed with a one-way valve to only let air in (to replace the volume of fuel being consumed), then something else must be responsible for letting air out when the tank gets pressurized. If I remove the one-way valve, then I may successfully create an exit path for the pressurized air (which solves my immediate goal), but I haven't then really addressed the issue of something else (whatever it is that should have been responsible for the outbound-venting the tank) being clogged or failing.

 

Anyway, any help appreciated!

 

Thanks,

 

Jake

[swooshdave]

I will say that with Italians bikes sometime you don't question why they did something and you just have to correct it. 

[inkblot]

@Swoosh: Ha! I hear ya...

[docc]

If you have a US spec fuel vapor evaporation system in place still, this is an example of after-engineering to meet US Federal nit-picking.

 

It weighs five pounds and includes twenty feet of 1/2 inch SAE fuel line to accomplish this, as well as the nefarious "one-way valve." It is "open to atmosphere", but only on the far side of all this plumbing, TWO carbon canisters, and vacuum applied from the intake manifolds.

 

I'm with Kiwi_Roy (always a safe bet! ) that something got pinched. *Might* be a good time for the Tank Off Maintenance Checklist with a good mind toward the venting/ overflow plumbing.

[Scud]

The emission system is different on the black-frame bikes (inkblot's is a 2004). There should be just one canister mounted in the exhaust hanger (behind the crossover). As I understand it, the European bikes did not even have hoses attached to the two vents under the tank. I have removed all vent/overflow/recovery hoses from mine - no problems so far.

[docc]

Thanks for clarifying, Scud!

[inkblot]

Hi All, thanks again for the help.

 

After reading Geddo's thread another 3 times (http://www.v11lemans.com/forums/index.php?showtopic=16618&hl=%20removing%20%20emissions&page=3) things starting making more sense- at least in the way that the tank vent and drain systems are supposed to work.

 

I ended up removing the one way valve and disconnecting the far end of that same hose from the charcoal canister. Now the tank can breath freely in either direction, and it appears that my problem is solved.

 

I found a few suspect things along the way:

- I think the one-way valve was installed backwards. If I understand correctly, it's purpose is to let air into the tank- not out- though mine was clearly oriented to let air out.

- The vent hose may have been getting pinched by the tank itself, as it ran down to the charcoal can. Hard to tell, but there were some suspicious wear marks.

 

I'm still not sure how either of these would fully explain the symptoms I had- but as Swooshdave says, don't ask too many questions Everything seems to be working, so I'll go with it!

 

Thanks again for the input.

 

Jake

[GuzziMoto]

Logic might suggest that the valve would be to let air INTO the tank, but I think for emissions purposes it was being used to only allow air to exit the tank towards the charcoal canister. But it is hard to know what an Italian is thinking sometimes. For emissions reasons they could not freely vent the fuel tank to atmosphere. They had to vent it to the charcoal canister in a controlled (read one way) manner. The charcoal canister would then, presumably, vent to the intake tract under vacuum. 

My guess is which way your one way valve was installed depended on the guy installing it. I am pretty sure some V11's had the valve installed in one direction while others had it installed the other way.

[inkblot]

Hey all- just a follow up on this story.

 

I thought I was all good, having bypassed the valve and charcoal canister. I definitely haven't had the tank pressurization problem since, but I do still have a drip of gas from the overflow line. I gave in and took the bike to the shop (Munroe Motors in SF, a generally reputable place that's always treated me well), and their diagnosis was that the hose inside the tank has rotted a bit do to sitting too long in old gas. This allows the fuel in the tank to slowly seep into the tube, and then out... Their quick fix was to plug the hose (funny how things come full circle, as the original problem was likely a clogged hose). So, now I have no leak, and hopefully no tank pressure issues either. Of course, I can't get the bike wet (for fear that water would find its way into the tank).

The only real way to fix the problem is to get a new tank, they said, as there's no way to get into an existing tank to repair the hose. Sadly, Guzzi doesn't keep stock of my tank anymore, so even if I wanted to spend the $, I'd have to source a used one (and likely have to custom paint it to match).

Anyway, I've decided to sell the bike, but before I do, does this seem to pass the sniff test to you all?

 

Thanks everyone,

 

Jake

[footgoose]

A hose rotting from sitting too long in old gas? hmmm... dunno about that one. How long did she sit?

 

Sad to see you're letting her go. I hope it isn't because of this little problem. Just like a 'delicate' lady, it takes some passion to get past the quirks, and the reward is so worth it.

 

there's a guy in socal that takes in wayward Geese.