Fuel tank vent

Hi there to the 5th gen community. I am hoping someone might offer some advice. My bike's fuel tank seems to overflow if i fill it past 14 liters. I first noticed it soon after i bought the bike about two months ago.

I filled the tank and it seemed to randomly dump fuel onto the tarmac until the tank was below half, on the gauge.

I had the tank off yesterday and pulled the pump mech and the gauge mech and found nothing, except that the tank was re-coated on the inside at some point and the gauge mech seems badly rusted.

By riding without the fairing for a bit, i have realized that the fuel drains via the vent pipe, which is the smaller diameter pipe of the two dedicated to venting or breathing. There is also an 8mm tube which is the overflow from the tank filler. It doesn't leak from there, but from the vent. I cannot figure out why or how come it would do that. Does the tank build up pressure ? How on earth would one remedy this ?

Any Ideas ?

Also the motor seems to be missing a bit after removing the tank. Is there a bleeding operation to the fuel delivery that i missed ?

I notice that no-one has replied to you, which is unusual for such a well informed and intentioned crowd, so I'm guessing none of us have had any experience with this problem. I'm certainly in that camp myself. As I understand it, the air vent in the tank should sit at or near the highest point in the tank, so it is impossible for fuel to exit the tank under normal conditions. If your vent has been relocated somehow (e.g. bent downwards) then I can imagine it would allow fuel to drain out when the sun or engine heat makes the fuel/vapours expand. There is no vent in the fuel cap, I know because you can happily park the fuel tank upside down when it is full.

Just for clarity, there are four hose connections to the tank. The high pressure fitting from the fuel pump to the rail, and then a low pressure return line from the pressure regulator. A large diameter drain for the filler neck, and then the (troublesome) air vent.

Hope you get this worked out.

I think the hose you refer to is the overflow, and connected to the little hole in the well around the tank filler (you see when you lift the cap).  In operation, the tank vents through a charcoal evaporative emissions canister, controlled by the ECM via a purge valve solenoid.  The tank does build low pressure in operation from the heated fuel (fuel cools the injectors).  I think you have a problem with the cap seal.  A quick look at the parts diagram does not show the seal itself.  You might need to buy a new cap assembly. 

I'm guessing that given the OP is in South Africa, his bike probably won't have a vapour canister, so the vent line will drain to atmosphere under the bike, as mine does. I'm confident that modern bike caps do not have any vent and the fuel cap should seal 100%, so you are reliant on the vent tube to release any pressure and allow air to enter the tank as the fuel load drops. If the vent line intake is sitting below the level of the fuel then the any pressure will cause that to push fuel out.

I noticed the OP mentioned that internals had been recoated.

If the tank had corrosion problems, hence the coating, it might have the breather pipe corroded below fuel height.

Nothing can fix this.

No bleeding needed, the fuel circulates through the return pipe.

And as far as I'm aware, California was the only place in the world that 5th gens had evap canisters, different ECU, as well as milder cams and less ignition advance.

Thank you very much for all the replies and your consideration. The line overflowing is definitely the vent and not the overflow. They are two separate lines and the one has a larger diameter. It is possible that the re-coating/repair was done without careful testing or checking. It seems par for the course in many instances. So at this point, i imagine that there is a break or crack or something in the vent line below the highest point on the vent installation in the tank. I have put an extended line onto the vent tube and coiled it up at the handlebars for now until a solution shows. I can hear bubbling when i blow on the tube so there it is. What a pain. I can imagine that the only solution is an alternative tank. Apparently those are like hens teeth round here. If anyone has any bright ideas, i'm all ears.

If you were able to access the inside of the tank through the pump flange, you may be able to slip some tube over the vent pipe and extend the height, or if it has a hole maybe block it along the length. I think it should terminate in the high point of the tank adjacent to the cap. Or you could go old school and install a a replacement vented cap with and seal off the original vent, e.g.:

http://www.ebay.com/itm/2003-2014-Honda-CBR600RR-CBR-600-Motorcycle-Race-Fuel-Gas-Cap-Billet-Keyless-/182578066028?var=&hash=item2a8280326c:m:m_yk3QPPbJuTd20zIk6plNA&vxp=mtr

Yeah the vent tube should rise inside the tank to a high point.

As Terry mentioned you could old school with a vented cap and seal off the old vent.

Or if you have the patience to remove the tank and pump again...

Check the tube length and where it terminates, or if there's a tube at all. You may be lucky enough to "bend" it back up higher.

Personally if I were to go to the trouble of removing everything, I would have the vent repaired/replaced and rewelded (not seen underneath)

The running of a hose higher than the tank would be a very short-term solution in order to have someone look at it, for me.

I wouldn't want the risk of having the hose spit/break or even the vent separate from the tank = fire

[image: fuelproblem.png]

What Vee-f-ar said, is good. But there are other options.  Lift the tank & remove the vent hose. using a small rod measure the length to the top of the tank & make a note. Now get a piece of thin wall SS tube a few mm shorter than the measured length of the correct diameter to just fit in the vent tube. Get some fuel proof adhesive & simply smear the outside of the new tube & insert it until flush with the bottom of the old vent pipe. Leave to harden & job done. 

Alternately, remove & empty the tank & fit a bolt through replacement vent tube. Either plug the old one or drill out & replace with the bolt through one.

Have fun