gas leak from vent line...ATTN SUPERBLING
 

since superbling seems to be the authority on our bikes, i hope he has an answer for me. i own a 1999 superhawk color black, bought her 4 years ago with 18000 miles, she now has 61000 miles. i have developed a strange fuel leak from the vent tube, not the over flow tube. when the bike sits in the sun with more than half a tank of gas, fuel will slowly leak from the vent tube. if i add air to the vent tube the tank will hold pressure until i let go of tube, air will release. if i add vacuum, the tank will NOT hold pressure nor will she pull fuel from the tank. can anyone help me with this problem? is the small nipple on the bottom of the tank the only vent for the tank? please help......

anybody?

I'm thinking a bad petcock... if it's leaking (vaccum part) then it might not hold once not under vaccum...

Try taking it apart anc cleaning it and have a look at the diaphragm...

I'm certainly no authority but I try to help when I can and there are plenty of other knowledgeable folks here. They don't call it WOTL (wisdom of the list) for nothing!

Unfortunately, I don't have an answer or even a suggestion for you at the moment. This is strange. It runs OK otherwise?

she runs perfect. it does not leak from the petcock it leaks at the small vent port under the tank. the reason i ask you superbling is that i know you have cut our tanks apart, my question is, where does that small nipple go inside the tank. when air is blown through the line, i can see air blowing out of a very small hole on the left side of the tank just as it starts to drop to the sides. air comes out of the hole but i cannot get fuel through it if i apply vaccum. i know the large line under the tank is the overflow, and i know the small line is the vent line, so where does it vent in the tank?

Your Avatar shows that you have a black bike which may be part of the reason for your problem. As your tank cools off at night fuel condenses in the vent line and is expelled the next time it's heated by direct sunlight.
The vent set-up on Honda's tanks is a small, vented, lentil shaped metal container near the top front of the fuel tank that is connected to the vent tube. That is the only place air should be coming from.
If you can actually see bubbles from the vent tube itself you may have a hairline crack in the tube that opens up when the tank/fuel expands in direct sunlight.
Let me try and take a look at my original tank tomorrow and see if I can figure out where yours is leaking.

Kai Ju

Had you recently taken the tank off for anything? Or did this problem just start out of no where?

No you have me confused with someone else. My VFR tank mod required absolutely NO cutting apart of the tank; only a small trimming of the rear tab/mount.

I do know if you turn the tank upside down and then back, gas will absolutely SPEW out the vent tube! BTDT LOL This leads me to believe it is near the top next to the opening. Kai will hopefully nail it down for us.

I'm the one who took a spare 98 VTR tank and cut off the top partially and added a periferal steel band to increase the height and thus the capacity. On the 98 tank, the vent line runs up to the 1 O'Clock position (1:20 to be precise) around the fuel filler opening beneath which a anular "saucer" collects gas vapor. If you over fill the tank or liquid gas sloshes into the saucer, or the gas expands due to heat and fills the saucer, it will drain out the vent line. The actual gas overflow hole is outside the filler opening and is designed to drain gas the spills over while fueling up. If the rubber seal on the gas cap does not leak once the tank is full, it cannot reach the fuel drain hole. However, if you still have the PAIR system, the gas tank vent hose tied into a T-fitting that also connects to a vent hose from the carbs. The T-fitting and routing of the hoses can cause stalling if the tank is over-filled because the hose routing sometimes creates a "P-trap" that prevents venting. Running the tank vent line directly from the underside tank vent nipple to the lower left front of the crankcase next to the lower engine cowl eliminates this P-trap. When filling the tank, you'll see a horizontal flat bar below and adjacent the filler opening. Fuel should not be filled very much above this bar; as it serves as a top-off fuel level indicator.

If you have a hole in the top of the vent tube below where it enters the bottom of the saucer, you will also have gas drain out the tank vent hose. If you somehow do have a hole and you can see and access it from the fuel filler opening with the gas cap assembly removed (do so by removing the 12, 5 and 7 O'Clock hex head cap screws that circle the gas cap ring, the others are "dummys"), it should solve this problem. Washing out the tank and low-temperature solder can be used to plug the hole (but be carefull not to block the ID of the tube), or a gas resistant epoxy "patch" may also do the trick.

I'm actually having problems getting my big tank to vent properly because when I stripped and seal coated with POR-15 US Std Tank Sealer a second time, a bit of the sealer partially plugged the end of the vent tube where it enters the saucer. I have devised a way to clear the blockage but have not executed the fix yet; which I actually planned on doing this weekend.