The Case of The Non-Venting Gas Tank

[billz410]

Here's a question for you gearheads-

Had the tank off my '08 Nomad and did the 7" filter modification, in addition to reed valve removal and also removed idle control solenoids.

After putting everything back together, I went to put gas in at the gas station and got quite a surprise when opening the gas cap- huge amounts of pressure built up in the gas tank. Not good.

Here's the deal-

On Gadget's website he talks about removing the charcoal canister on CA Emission bikes when doing the air cleaner mod- often done in conjuction with the installation of coaster plates, etc.

He provides instructions to just connect the two hoses going in and out of the canister- making a 'loop' of sorts. However, my left side cover is filled with vacuum servo for cruise, fuse panel, TFi, etc., so canister was completely removed.

You will note on the Vacuum Hose Routing Diagram on the inside left cover that a green-labeled hose from the canister goes to the air cleaner- this hose was completely removed because of the new backing plate from Chuckster.

You then have a blue-labeled hose from the canister which goes to the 'return pump'. This hose I have vented to atmosphere right now. ( I had it plugged- didn't affect the pressurizing of the gas tank.)

Next is a red hose and a blue hose from the return pump that go to the rear of the tank- those are hooked up correctly.

Then there is the white-labeled hose from the return pump that runs up to the throttle body area- also hooked up correctly.

And, at the front of the tank is the 'dribble' hose, for those times you overfill your gas tank. This hose is not plugged.

Any ideas on why my tank is pressurizing? It builds pressure almost instantly when the engine is started- and of course takes even less time to pressurize when the tank is full.

I no ace mechanic, but I just don't see what I can have hooked up wrong in the way of hoses... any of you ever had the your tank pressurize in this manner? It's substantial pressure- very definitely something wrong.



Thanks,

[AlabamaNomadRider]

Did your bike build pressure before all of the above mentioned things were completed? I know the other guys will probably want to know that. I have an '08 also but have not done any of the things you have accomplished. Just so you will know, my bike does tend to build pressure. I know I filled up one day and came home after filling and it is only about a mile from the house. I thought I would check and see the level in my tank. I got quite a surprise when I opened the filler and gas and air went everywhere. If given time I think your bike will let the pressure off. I know mine does when it sits in the carport. It will whistle for several minutes but eventually it lets the pressure off. Sorry I can't really help you more than that but some of the other guys will be able to. The more information they have the more they can help.

[billz410]

I understand what you're saying, but the bike never did this in the past, even when the weather was hot. I'm talking about the kind of pressure that can blow the lid back and spray you with gas. I find it hard to believe that's normal.

[AlabamaNomadRider]

No, if it didn't do it before then something happened. Is it possible the vent tube got kinked or something?

[ringadingh]

Check the gas cap, I think there is supposed to be a vent in it to prevent this. It would be the same vent that causes our bikes to whistle. there is a article about working on them on Gadgets sight that you could check.

[dogdoc]

I would tend to agree with Gene. Vent tube could have goten back on and kinked, this would notallow the tank to breath.

[billz410]

I'll check that out, ringadingh. It was suggested to me that I 'modify' the gas cap in an effort to alleviate the high-pressure problem.... strange that this problem only occured after removing the air switching valve and other assorted paraphanelia.

I can remember the bike whistling in the past after I'd shut it off- but the tank never built up pressure like this!

I checked the springs in gas cap, they seem 'springy'- I assume the cap works sort of along the lines of a radiator cap.

[macmac]

Are you right side intake now, with no black plastic cross over air tube?

[billz410]

Yes, that's right, Mac. Crossover tube has been completely removed. Sure curious to hear your thoughts on this.

I'll add that when I shut the bike off, I don't get the 'whistling' gas cap like I did before the modifications. You'd think it'd be whistling like a tea kettle with the amount of pressure released when I opened the cap.

Gas will still seep out of the front overflow hose if overfilling the tank, etc.

[macmac]

Hmmm, If and when fuel seeps out the front over flow, my take is you mean the forward right side as seated tubing, ALL the way up front.

In a way I hope I am wrong. If I am correct and you do mean this, then it has to be one of twoo things wrong. The first one i choose will be the best case senario. And the cap seal would be the culprit, which isn't a bad thing since you have over pressure.

So probably the cap seal just can't deal with this situation.

The worst case senaroi is the line inside the tank has a bad problem, but isn't very likey.. The reasons for this is that is a car wash, rain water drain.. The open hole under the cap is a catch all for water on top of the cap and the tank as water run off..

So long as you mean the rubber tubbing way up front.


What I think the real problem is, is the cap vent set up but chit luck has gagged up and you need to pull the cap assemble and mess about with the clear plastic seal valve thingy's That high tech talk fer what them things are see

Now I have only worked on one cali bike and it belongs to Flavor.

At the rear end of the tank there is a pair of fittings alike other than red and blue color coded tape.

When his bike was done the red fitting was capped off directloy at the tank with a heavy duty cap from a kit you can buy at NAPA. This is just a better cap for fuel and fumes in my opinion, thicker rubber too.

The fitting marked blue got a standard fuel line and was vented like non cali bikes direct, following the same routing.

What I think you are calling a pump is a 'Separator' and on his 07 bike that was marked green not white... I find that very odd, but I don't know what year your bike is..

He lost every single part you did, and they were cardboard boxed up and stored.

I am not sure I like the loop idea either, and would suggest you do two things..

Cap off the red fitting at the tank, adding a line to the blue, like any other Nomad.

And check the cap vent directly as a separate problem..

[macmac]

Another theory: The cap vent has been bad a long time, and over looked because most venting is done via the Seperator and the tubing to the black plastic cross over tube.. So long as the engine is and was just running and will be again soon the system has/ had an active device to remove and recirculate fumes and so pressure with in the system...

I am dang sure Flavor had no issue since this job was done. It was done before his trip west...

[billz410]

Thanks for the input here Mac.

Just to double check and satisfy my own curiosity, I took off that hose at the front of the tank- the one for the overflow- and blew air through it. I felt certain there was no obstruction here because I had watched drops of gasoline come out the bottom earlier- but I did it anyways.

Then I blew air through the short section of plumbing on the tank overflow- no obstruction there. That meant to me the problem must be in the cap. I was about to try Gadget's shorten-the-spring idea, but decided to put the cap back together without any changes, and go for a test run.

I went a mile or two and opened the cap, expecting it to blow my head off like before, but there was only a minimal amount of pressure. Eventually, I rode for about an hour, and then let the bike sit in the hot sun, and when removing the gas cap I had just minimal pressure- normal.

So, it would seem the mechanics of the cap must've been stuck. As you said, the cap vent set up. The tank had been off the bike for about 6 weeks just sitting around.....

I wonder what would have given way first had I not opened the gas cap?

[macmac]

Does this mean you dicovered the water drain for car washings and rain? Perhaps you took water for fuel draining?

I am not familar with Az, but should think sand storms might clog things.. Pine needles here do all the time on everthing, as does lots of bigger leaves that some how pass screens on car and truck intake venting.

When I saw pine needles I mean a lot more kinds of trees than just pines.. But bigger leaves also clog drains with screens to prevent this, but still some how they do.

I posted with a bit too much haste, and checked out more after, but yesterday was a long day with 7 straight hours of driving a truck down to the flats of Mass, thence to Maine before homeward bound.

The is a real live vac hose that runs the separator, and you want that gone and capped off at the throttle body near where the reed valves have a fitting which should be capped off as well, removing all that crap...

Whether ir not the problem went away you should do what I said above and create a rear tank drain like any non-cal modle has, and cap off the return.

What might be possible is in doing this work a bit more fuel than the breather with the spring gadjet mentions was soaked and so sealed tight. Something like wet books do, and it makes it hard to open one page sealed to the next.

Perhaps the combination of the spring which assists the seal and extra fuel caused the system to gag..

[billz410]

OK, Mac, will do. I'm wondering- does a guy even need that seperator on the bike at all? There's not much left in the way of hoses that are hooked up to it!!

[macmac]

No... take it off.. You took off the cross over tube right? The same for the carbon canister, so get them off, and get off the pod that is under the tank to the reed valves too.. You added coasters right?

With all that gone you should end up with a capped off red fitting at the tank a blue fitting at the tank will have a longer drain hose running down with the coolant over flow, side by side terminating near the oil filter in the retainer there.

The throttle body will have 2 ports capped off, one where the white tubing was, and the other where the vac pod line was.