tank suck

[rossi46]

Hi guys I came home from a ride the other day and whilst in the garage I thought I would add some redex in the tank, I always ride with ear plugs and have never noticed this before but when I opened the gas cap there was a distinct rush of air! is normal  thanks

[Desdinova]

Sounds like the vent is clogged

[docc]

What year is your V11? (consider adding that to your profile)

 

The early 1999-2002 tanks with chin pad and external filter have a vent with a one way valve under the tank. The valve can become disoriented or the lines clogged. (easy fix). Some remove the valve altogether. Quick fix is to remove the small rubber washer/seal visible when the filler cap is open. Either of the last two methods may allow fuel to spill if the bike becomes horizontal.

 

I'm not sure if the later, pump-inside, tanks still have the same venting system?

[rossi46]

Thanks guys, Docc it's a '01 external pump, do you mean the domed rubber piece that is on the rear of the filler cap it self?just remove this? where is the one way valve? thanks

[docc]

"the domed rubber piece that is on the rear of the filler cap"

 

Yeah, that's it. Breaks the seal between the tank and the vent. I wouldn't call it a permanent solution; more of a "field expedient."

 

That tract leads to a nipple under the tank (the other is for the fuel overflow, also visible under the filler cap). Factory stock, these two tank nipples drop separate vent hoses to below and behind the sump, the tank vent through a small plastic disc valve about an inch in diameter. They are prone to failure as is the tubing prone to clogging.

 

Part of the Tank Off Maintenance Checklist . . . .

 

">As the tank goes back on, re-secure the tank vent and overflow on the underside of the tank. This is fiddly and the connections may benefit from using small wire clamps that will still allow a press fit. There have been many modifications reported on this routing, but simply be certain your tank vent and overflow route below the engine and exhaust not onto them, even if they are co-joined into one drain tube. The factory fitting has a one way valve (small plastic disc) that can become disoriented or obstructed and allow a vacuum to build in the tank. Make sure the valve is oriented for vertical flow and secured. If your tank has suction when you open the filler cap, the venting needs to be addressed. One quick-fix is to open the cap and remove the small rubber seal on the right rear of the cap. I'm not saying it's a good idea, but it has been used as a quick fix."

[rossi46]

thanks (again!) Docc both my V11's never had any plumbing under the tank! I have run a fuel line from the over flow down the back of the g/box , no sign of the plastic disc you mention!

[docc]

Both the nipples facing down and forward under the tank had no hoses on them? Originally they would have had ~1/4" lines routed to the left behind the starter.

 

Make sure the internal drain and vent from under the cap are clear through the nipples; compressed air would likely work, although a spray solvent might be necessary if they've clogged.

[Scud]

I think the LEFT (assuming seated on bike) nipple drains water out from the fuel filler - from rain, washing, etc. The RIGHT is to let air back into the tank as the fuel is used (thus preventing vapor-lock and tank-suck). From what I can gather, the RH had a hose only in North America (to comply with California's rules and make the bikes "50-state" compliant). Most people in Europe said they never had anything connected there from the start. In the US, the hose from the RH went to the evaporation canister (also not available in Europe). These canisters were so fragilely mounted on my bikes that they both fell off...

 

As for solvent, what would you use?  Throttle body cleaner maybe?  I assume it should be something that you'd be willing to run through the fuel system.

[docc]

Correct, the left is the drain; for unwanted water around the filler, yes, but also any fuel spill from refueling. I would think this especially warrants routing to below the (hot) engine and exhaust.

 

Interesting that the non-US spec bikes simply have an open nipple on the right (confirmation from our world community?). I entirely forgot about the charcoal canisters being the destination for that routing after the one-way valve.

 

This makes me consider opening the right nipple and stop fussing with Y-ing it into the drain.

 

So, very likely, rossi46's UK Guzzi simply has an open nipple? Makes sense: no charcoal fuel evaporation recovery debacle.

 

For spray solvent, I prefer CRC Electronics Cleaner. Not so caustic as throttle body, carb, or (especially) brake cleaner - evaps quickly and cleanly and is kind(er) to painted surfaces.

 

I just wonder if the exposed vent nipple may be more susceptible to clogging under the tank than if it has a bit of hose pushed on it?

[rossi46]

thanks gents, yes Docc  no hose at all! I think mr. Roper mentioned a customer 's bike that had a fiery end because of no drain hose and fuel dripped out onto hot engine so have installed a hose on the left nipple, will whip my tank of on the w/end-I wonder if this caused my poor running when at altitude in Europe?

[Kiwi_Roy]

Your ECU has a barometric sensor that's supposed to take care of altitude, is it possible that's plugged off?

 

 

Sent from my shoe phone!

[rossi46]

thanks Roy where would that be?

[Kiwi_Roy]

Right inside on the circuit board, small round thing.

[rossi46]

I take it its not serviceable then? how do i verify that this is the issue? what would be the solution?(new ECU,)Is a repair likely?

[Kiwi_Roy]

I very much doubt the sensor failed, they are available because I bought one to replace the original I robbed for the MyECU.

 

I wonder if GuzziDiag has a readout for Altitude, if so you could suck on the sensor to prove it out.

 

If the vent was blocked off I would fix that first, the fuel pump may have been starved with the combination of high elevation and tank suck.

Do you recall if it ran better some times, like after filling up?