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Gas leaking out of vent hoses

R

RTandGS

New member
So just recently at fuel up gas will leak out of both tubes until the fuel level in the tank gets lower. Made me think the in bed vent hoses came loose. I opened the tank and the lines are secure top and bottom. I didn’t blow air through the hoses at the time but a hole in the hoses, both of them, can be the only reason, am I right about that?

Thanks.
 
Happens to me: Fill tank right full with cold fuel, add heat from the sun when parked=gas puddle.

I just adjust how much fuel I put in when I know the bike will be parked for a time or I fill it right full and then turn the throttle and go through the gears until I need more fuel or stop to pee.
 
Is that the deal that saturates the canister? Filling the tank extra full?
OM
 
mykrs said:
So just recently at fuel up gas will leak out of both tubes until the fuel level in the tank gets lower. Made me think the in bed vent hoses came loose. I opened the tank and the lines are secure top and bottom. I didn’t blow air through the hoses at the time but a hole in the hoses, both of them, can be the only reason, am I right about that?
Click to expand...

I would suspect the two vent hoses submerged inside the tank. They may still be fastened tightly at their ends but the hoses may have cracked from age. Note that if you decide to replace them you’ll want submersible-rated (SAE 30R10) hose. Those lines are 5mmID x 10mmOD; bulk line is available in one-meter lengths from BMW. New clamps are a good idea, too—the OEM Oetiker clamps are a pain to work with but do the job well.

Best,
DeVern
 
Last edited:
Omega Man said:
Is that the deal that saturates the canister? Filling the tank extra full?
OM
Click to expand...

Several things can do that. Filling the tank until fuel nearly overflows the “biscuit” vent-separator in the tank can do it, tho it is physically difficult to fill a tank that full. Other causes can include a biscuit that has fallen loose, a cracked or broken purge hose inside the tank (the one that’s connecting the cannister to the biscuit), a broken/dislodged/missing/poorly-replaced clamp on the purge line inside the tank, or misconnected vent and purge hoses (cross-connected). That latter one can contaminate the cannister with H2O draining down from around the fuel cap.

But if one has a saturated cannister the usual approach is not to check the above, but to do a cannisterectomy. Which of course leads to that faint hint of gas fumes in the garage the morning after a fuel-up, and the nagging worry as to how that meshes with the gas-fired water heater mounted in the garage. But, I digress. :)

Best,
DeVern
 
Or, It could be as simple as the tank is plastic, you put cold fuel in it, it shrinks, the sun warms it, the tank expands, so does the respective volume of fuel, pressure builds, exceeds the fuel cap relief capacity or even the fuel tank volume?
 
This happens to me only when I have filled to the top in morning on way into work and I leave on side stand instead of on center stand. No over flow on center stand.
 
chrisinsc said:
This happens to me only when I have filled to the top in morning on way into work and I leave on side stand instead of on center stand. No over flow on center stand.
Click to expand...

That makes sense. On a full-to-the-top fillup, putting the bike on the sidestand dips the biscuit into the fuel and even tho the vent hole is on top of the biscuit it can be submerged and drain raw gasoline into the canister.

Best,
DeVern
 
Well I have filled the tank with just 3 gallons of gas and I still get the leak...so I have to assume that BOTH of the vent hoses in the tank have cracked at the same time? They're both connected top and bottom to fittings. So, that's my working theory.
Now...
Has anyone discovered submersible 5mm vent hose for less than $20 a foot? and I'm assuming I need 3 feet. Yikes!
Thanks!
 
I use BMW Motorworks UK for almost all my parts even though I am in the US. 2 day service for very reasonable prices. They also have a large selection of used parts.
 
mykrs said:
Well I have filled the tank with just 3 gallons of gas and I still get the leak...so I have to assume that BOTH of the vent hoses in the tank have cracked at the same time? They're both connected top and bottom to fittings. So, that's my working theory.
Now...
Has anyone discovered submersible 5mm vent hose for less than $20 a foot? and I'm assuming I need 3 feet. Yikes!
Thanks!
Click to expand...

You’re on the right track now. I got a one meter length of hose from max bmw, that I cut in half and it just fit.

When did you last replace the u-shaped hose?
 
roger 04 rt said:
You’re on the right track now. I got a one meter length of hose from max bmw, that I cut in half and it just fit.

When did you last replace the u-shaped hose?
Click to expand...

I never replaced the ushaped hose. I just got the bike.

Max BMW, thanks, having a look. I went to a used bike shop today and bought some stuff for my bike at great prices and damn if he didn't cut those hoses when he removed the fuel pump to sell it. But i got a clean wind shield for $20, so that was a win.
 
Ordered hose from motor works in the UK. Even with shipping, how can it be cheaper than the US? It is, so I’m trying them out. Will update.
 
Tank vent hose

I replaced my expensive rubber hoses that turned to dust in the tank with Tygon 4040 fuel line. Been over a year now with no issues.

You can buy it on ebay, cheap.
 
A little confused

Are you looking through the gas filler hole to inspect the vent hoses? Have you removed the tank and are examining the vent hoses?
I live in Tucson and the heat is serious. Fill on side stand, let pump hit stop, don't try to cram more in. Problem solved. (o, and **** canned the evap canister)

I was just inside of mine and found a good tip- secure the vent hoses with a tie wrap. A little better than just being held with friction.
 
m4bmw said:
I replaced my expensive rubber hoses that turned to dust in the tank with Tygon 4040 fuel line. Been over a year now with no issues.

You can buy it on ebay, cheap.
Click to expand...

Ah! Thanks I wish I knew! I bought the expensive hose already but for the future.
 
Update

So today I opened the tank and swapped out the vent hoses, I reused the factory clamps which wasn't that big a hassle actually. I went and filled the tank with gas and rode home. and so far...no gas coming from the vent hoses. Hopefully that is problem solved. I bought the hose from the UK BMW. With shipping it was $12 less than EME, how can they do that?
 
m4bmw said:
I replaced my expensive rubber hoses that turned to dust in the tank with Tygon 4040 fuel line. Been over a year now with no issues.

You can buy it on ebay, cheap.
Click to expand...

Give it another year it will harden.
It is not rated for continual submersion.
I learned this from firsthand experience.
 
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