Fuel tank vent issue

J

J.B.

fast rider
Joined
Mar 17, 2022
Messages
50
Location
Massachusetts
Hi,
My 2002 401 seems to have a bit of an issue with fuel tank vent. The gas cap, when opening it, it is sucked onto the tank, and that tellale sucking noise of the air rushing in as I open it. It hasn't caused any running issues so far, but was wondering what is going on. The bike has the EVAP canister removed, but it did the same before the removal. If you have an suggestion, please let me know.
Thanks!
 
Hi,
I had the same issue. My vent pipe underneath the tank was pinched. I removed the fairings, loosened the tank and "removed" the kink. Now it should breath again.
Regards
 
Interesting. I’m having issues with my 2022 svartpilen 401. It has a flat spot in 1st gear at higher rpm just before I shift to 2nd and it appears to get worse and does the same thing as I go through the gears the longer I ride. The dealer plugged it in and found nothing. Could it be as simple as a tank vent issue?
 
I checked the vent hose last night, and it was fine. I haven't ridden it since yet (it's stormy out all). I don't think it has affected the driveability, or at least not that I noticed, just a negative pressure in the tank. So far.
 
The vent system is complicated... and includes an electronic valve.
1651952801055.jpg

But there is always this:
smartmoto-electronics.com

EVAP / Canister Removal kit PVE-031

The EVAP / Canister Removal kit by SmartMoto eliminates the standard EVAP system.Motorcycle manufacturers install the EVAP system to prevent fuel vapours from escaping to the atmosphere. This is good for emissions but converting a bike for trackdays or off-road use means you need to shed as much wei
smartmoto-electronics.com smartmoto-electronics.com
 
Mine has that EVAP removal kit. But it was doing the same before I installed the removal kit. I was hoping that removing the EVAP system would cure it, but alas.
 
There is a hole to the tank with a rubber grommet that I think mates with an air bleeder valve in the cap? Might be worth making sure those are clear and clean.
My next step would be disassembling the cap to see the vent passage. If you do that please post pictures!
PXL_20220507_213054145.jpg
 
Yeah, that line is clear. So as you say, I may have to take a look at the fuel cap...but I wish I know what the vent passage should look like! But yeah, if/when I take apart the fuel cap, I'll post pics.
 
I am a bit confused... reading from the start...

So, the only issue is a noise of air when opening the tank.

Doesnt every fuel tank do that?

The pressure release is just a valve, so it doesnt blow up when you park in the sun. And so long as the pressure is below the "over-pressure" limit, the release should not release.

Those things are pretty simple in design...

And I would expect it to always make a suck or blow noise depending on the differences in atmosphere outside the tank, and inside the tank.
Unless you just opened it less than five minutes ago, there is always a difference between inside the tank and outside the tank.

OR am I misinterpreting the initial post?
🙃
 
BISavage said:
I am a bit confused... reading from the start...

So, the only issue is a noise of air when opening the tank.

Doesnt every fuel tank do that?

The pressure release is just a valve, so it doesnt blow up when you park in the sun. And so long as the pressure is below the "over-pressure" limit, the release should not release.

Those things are pretty simple in design...

And I would expect it to always make a suck or blow noise depending on the differences in atmosphere outside the tank, and inside the tank.
Unless you just opened it less than five minutes ago, there is always a difference between inside the tank and outside the tank.

OR am I misinterpreting the initial post?
🙃
Click to expand...
There shouldn't be negative pressure inside of a vented fuel tank. That's what the vent is for, so the fuel gets used, and the space the fuel occupied is filled instead of the same amount of air, basically. The fact that there's negative pressure means that the air is not getting in there to maintain atmospheric pressure. Negative pressure inside the vented fuel tank can cause fuel supply issue. Also, with evap removed, there's no vent valve, just a straight open line, so I'm guessing the issue is either the vent passage of the fuel cap is clogged, or it's not seating on the rubber bit properly, or something like that.
 
I was under the impression there was always a "small" pressure difference... normally when there is a problem it dents-in or blows-out the tank...

Everytime I open anything I fill up with fuel, it makes a "shhhhsssshhh" noise.

Again, I do not claim to be an expert or a specialist.
 
Maybe the valve only opens when the vehicle is running? And then if the tank cools after a ride it generates negative pressure that is maybe relieved when the bike is started?
 
Mmmmmm.......
There's an evap valve that is electronically operated, to which the vacuum line connects to. That is removed as part of the evap removal. The vent line is now just open to the atmosphere, so...it's a bit of a mystery.
 
When I had the kink in the vent line, there was always a "shhhh" and the fuel cap was hard to open (had to pull it quite a bit).
Since I "unkinked" it I can blow throug the fuel vent pipe (Vintage Veloce post #10) which I could not before. And there is no "shhhhh" anymore and the fuel cap is opend very easely.
This on a stock 401 with the evap still in place..
 
It was kinks in the vent line. When I blew compressed air through it from the rubber nipple in the fuel cap area, it goes through fine. But that line is not blowing air from the tank, but sucking air into the tank. When I first lifted the tank, I couldn’t tell is there was and kink in the line, as a matter of fact, it looked fine. But i kept on having the same issue, I took another look at it, and there it was, it was pinched by cables and whatnot in two places. I freed it up and it’s good now, but I need to replace the hose - it’s no longer pinched but the hose has permanent kinks in it. I don’t know about others, but these kinds of little quality issues are so annoying. So yeah, if your tank builds up negative pressure, the vent hose is the likely candidate.
 
J.B. said:
It was kinks in the vent line. When I blew compressed air through it from the rubber nipple in the fuel cap area, it goes through fine. But that line is not blowing air from the tank, but sucking air into the tank. When I first lifted the tank, I couldn’t tell is there was and kink in the line, as a matter of fact, it looked fine. But i kept on having the same issue, I took another look at it, and there it was, it was pinched by cables and whatnot in two places. I freed it up and it’s good now, but I need to replace the hose - it’s no longer pinched but the hose has permanent kinks in it. I don’t know about others, but these kinds of little quality issues are so annoying. So yeah, if your tank builds up negative pressure, the vent hose is the likely candidate.
Click to expand...
Great follow up! Good stuff to know.
 
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