My motorcycle is incontinent.

[marshall]

Prefix: This turned into a long post, so here is the gist of it:
-My carb #1 was pouring fuel out when the left hand fuel petcock was "ON" (engine off), but magically did NOT leak any fuel when the petcock was on "PRI." You'd think it would be the other way around, if anything.
-There was no sign of anything stopping the float needle from closing, so there's no explanation for why it was leaking.

Yesterday my 80 XS started leaking gas in a very bizarre way after having no problems whatsoever in the past. I would have posted last night when the events of the day were fresh in my mind, but I was very frustrated and it would have turned into a rant... So I'll do my best to recount the order of events here. I am really at a loss as to what is going on, but I'll do some more investigation today.

In the morning I finished changing valve shims, then synchronized the carbs and set the air mixture screws.

Then I decided to go to the store and buy some fasteners, so I got on the bike and started riding.

About a mile later, I'm losing power so I pull over to see what new treat my XS has in store for me. Dumb me; I had left the fuel petcocks on "OFF," and I had just run through the gas that was already in the bowls. I figure no biggie, this certainly wasn't the first time it's happened, so I turn the petcocks to "PRI" and wait a few minutes for the bowls to fill.

Now I'm a little fuzzy on this part, but at some point I may have switched the valve between "PRI" and "ON." Regardless, I'm about to go on my way when I notice a dripping noise and unscrew my air box to find that it's filling up with fuel. The fuel is dripping out of the #1 (left hand side) carb intake tube. I immediately start rapping the side of the float bowl hard with a wrench, thinking some dirt was caught in the float valve. The leaking doesn't stop until I turn the fuel valves to "OFF" and wait a little while.

After rapping the float bowl and trying different petcock positions, I got the impression that the problem had fixed itself, because carb 1 wasn't leaking anymore.

I continued to the store, parked, and (stupidly) left both petcocks in the "ON" position, because I've always thought my octopus worked properly. 20 minutes later I come out and there is a BIG puddle of gasoline underneath the bike. I scramble to turn the valves to "OFF" and take off the air box lower half. A large volume of fuel has leaked over 20 minutes and it takes a while for it to stop after turning the valves to "OFF."

Here's the weird part. After things dry out, I try playing with the left hand valve positions. In "ON," fuel practically pours straight through carb 1. In "PRI," no leakage. I am totally confused.

I ride the bike home on "PRI," turn the valves to "OFF" and go inside for a minute. When I come out, the gas is leaking again! This time both valves are in the "OFF" position and it's still leaking as if there was no float needle at all, despite all my tapping of the float bowl. I finally am only able to stop it by vice-gripping the fuel line right before it gets to the T between carbs 1 and 2.

I remove the carb 1 float bowl, float, needle and float valve body, and find NO sign of any blockage or debris or anything. I have 1 in-line fuel filter on each side that seem to be doing a good job.

Basically, at that point I was fed up and needed to get my mind off the bike, so I put the float + bowl back together and threw a tarp over the freakin' thing.

If the fuel tank cap vent was clogged, could that cause a carb to leak gas? I'm thinking maybe there was too much pressure in the tank?

Marshall

[CatatonicBug]

I would check 3 things, because it may just be multiple things working together, against you.
1. Take the petcock apart, and make sure the rubber "valve" is inserted properly and is not falling apart.
2. open the Octy and make sure that it's sealing properly. The rubber may be torn or just worn out.
3. Make sure the fuel hoses are attached to the correct ports on the petcock.

[Ivan]

I bet you have two things wrong.

1) Sticking float or needle on #1 carb

2) your hoses are reversed, such that on is actually prime and vice versa. Your octy is stopping the fuel in Prime, and not in on.

[Dragon Tamer]

The other thing that could be happening here is that the petcocks are not in the proper place like you think they are. Remember that the HANDLE points to the indicated setting.
I drove my first XS many years with the petcock in the wrong setting and did not discover my error until the first time I ran out of gas, I thought that I was in the "on" position and just then discovered that I had been running on reserve for years.
Regardless, you still must have some problem with the carb or it would not be leaking. My "octy" has been gone for some years now and I rarely shut the fuel off and only once had a carb leak when it got some junk in the needle valve.
Best way to find out is to bench test the carbs to see if they are leaking, I know it is a PITA but once the problem is found it is easier to fix it at that point with the carbs on the bench.

[Dragon Tamer]

Oh, and check your oil for gasoline contamination before you run the engine again!!!!

[John]

Let's make that three

I bet you have two things wrong.

1) Sticking float or needle on #1 carb

2) your hoses are reversed, such that on is actually prime and vice versa. Your octy is stopping the fuel in Prime, and not in on.

3) One adjustment that isn't found in any manual is the 'float drop setting'. When the bowls are empty, the floats naturally drop as far as possible. Sometimes that is too much, and the float needle can become cocked in the seat, and once the fuel has reached it's normal level, the needle is stuck open allowing the fuel to just pour in. The way to check this is, with the bowls off, hold the carbs in the upright position, and look at the needle. Does it look cocked in the seat? If it does, locate the small tab on the float where it contacts the float post, and bend it towards the post to raise the float drop limit, and not allow the needle to get cocked in the seat.
I learned this the hard way years ago. If you do a search for 'float drop' it should pull up some pics showing the cocked needle and how to correct it.