Okay... quick background. I have a 2001 CBR 600 F4i. I've had the bike for almost 3 years. Recently had the bike sitting for 6 months, so when I got back into the country I brought the bike to a local shop (reviews on their work was 50/50) for some minor maintenance.

They flushed the fuel tank, put on a new front tire, changed spark plugs, changed oil, and put on a new battery, and lubed chain.

The bike ran like a champ before I put it up for 6 months. While I was gone I used STABIL to protect the tank from corrosion. When they called me to come pick up the bike from the shop, they mention there is a leak at the fuel vent line, inside the tank... suggesting there was a small hole in the tank (perhaps from corrosion) that was allowing fuel to seep out once the tank was filled over half way. I was surprised to hear this, but afterall it was 6 months with no TLC in TX heat. Because of the hole in the tank I was told I would not be able to fill my tank above "halfway" without it leaking... unless i wanted to purchase a new tank. And they said there was no way of patching the hole from the inside? Not really understanding how the vent line works I could not really take much of a stance on the matter, and was in a rush to get to a family matter.

Later, I took the bike home, tried filling up the tank a little to observe the leak, and it leaked. However the way they described it to me was that the fuel was leaking directly from the tank through a hole near the vent line. The fuel is actually coming from this rubber hose below the bike (fuel vent line, i assume?). Its just a black rubber hose that dangles below the bike about 5" from the ground, and centered below the tank/seat area... which I never noticed before. It is uncapped.

I'm not too mechanically inclined obviously and plan to take the bike back to the shop for a better understanding of their description of the failure. But before I do, I was hoping to get some opinions as to what could be the possible problem.

My questions are...

Is this line that dangles below the bike a fuel vent line? If not, what is it?

Should there be any fuel coming from this dangling hose? (i assume not)

What could cause the fuel to get inside the hose?

I thought maybe as a quick fix, I could plug the hose, and this would keep it from leaking out. But again, not understanding how the tank is configured I thought it would be best to avoid any mechanical manipulation from my inexperienced ***.



Any help would be greatly appreciated!

-Joe

 

DO NOT PLUG THE VENT !!!!!!!!! Im on my iphone out on my bike, Im sure someone will tell u why.

 

If you plug the vent line, your bike will not run after a few minutes as gas flow will stop. It needs the vent line as gas is pulled from the tank, it has to be replaced with air, if there is no air able to be replaced, gas cannot flow.

there is a vent line, but also it could be the gas overflow line. If they flushed the tank and spilled gas into the overflow portion of the tank, it will leak fuel for a few days. Depending on how much they spilled over, it may take longer. It will eventually dry up and or leak out the line. In fact, I would guess the reason you saw the leak when you filled up is you popped open the gas cap, and the introduced more air into the overflow, which allowed the gas to leak out some more. When at home, pop open your gas cap and let it sit for a few minutes. If gas dripps out, let the cap open until it stops. This should allow most of the gas to leak out. Then go fill it up again and see what happens.

Im not sure how the vent line would leak gas out, as its only vent line, and should be at the top of the tank. It should not be below the level of the tanks fuel at any time. Unless the hole in the tank is leaking gas into the overflow portion of the tank, and thats the line that is leaking.

But, my guess is spilled gas into the overflow.

 

Thanks for the suggestion, but the bike is only leaking when new fuel is introduced. I tried leaving the cap open, but no gas leaked out. I put some fuel in there and it started dripping out again. It must be a very small leak because it is a really slow drip that comes out of the tube below the bike.

I am still unsure of how the tank is configured, but after hearing your response I am thinking there is a hole in the partition that divides the overflow from the tank (or reserve, depending on location of overflow). This will constantly provide a source to the overflow portion until a level of fuel is maintained below the vertical height of the hole.

can't something like this be patched?

 

OR... if this line is in fact the overflow line (and NOT the vent line), the hose could be plugged at the bottom which would then act as an extended overflow reservoir. Unless it is pressure balanced?

 

perhaps unrelated to this thread but relating to the vent hose, would it be inadvisable to filter the vent tube to keep sediment from getting sucked in and building up in the tank. I notice I as well need a tank flush. would this help preven this or restrict it's purpose too much?

 

I have the same exact issue with my 94 CBR 600 F2. If i put more then about 1.5 gallons into the tank it will drip rapidly from this vent tube. There is corrosion in the tank, due to it not being winterized for a little while, and it was suggested that i use a tank treatment to correct that but if there is already a small hole in the tank then it would seem that a full replacement would be best.

Has anyone else seen this issue or know if the treatment will help or if the best option is full tank replacement?

 

I believe I'm having a similar issue with my tank ('95 F3). the overflow line (the line that runs through the tank to the bottom of the bike and is attached to the overflow hole at the top of the tank) has atleast one hole in it I found running a small flexible cable through it. This causes my bike to leak fuel out the bottom once my tank is about 1/2 full.

It sounds like this is similar to your problem. I'm working up a fix for it so I don't have to buy a new tank but I'm not going to get around to it till August. My ideas to fix it are this, take of the tank and try to run a small rubber hose inside the old line running through the tank or just run a whole new line through it. and leave the old line in there.

You can seal off the bottom of the overflow line I'm talking about. Just fold over the bottom rubber part hanging at the bottom of the bike and zip tie it. Be sure to open it up and let it drain after it rains and every few days. I had my line that for the past 3 weeks and it ran fine.

EDIT: Btw if it's already leaking I don't think treatment will help since it's already got a hole in it somewhere.

 

and new tank and fixed.