Gas pouring from carbs.

[Wolf]

Hi everyone.
This winter i began rebuilding my recently bought '78 XS1100 E.
After putting things back together, i noticed gas dripping out of the pod filters on carbs 3+4 when shutting off the bike. First time i had this problem.
After a little searching on danish forums i found out that right petcock was leaking gas so it has been replaced with a functioning one.
Other issue i noticed was that the floats might not be working since fuel was overflowing. Carbs were disassembled and inspected (blow test), floats were adjusted, and everything looks ok.
New test ride, and trouble seems to be even worse than before! When shutting off the engine and leaving bike on kickstand, gas will start pouring out of filters 3+4 after a couple of seconds. Funny thing is that it seems to stop if i tilt the bike to upright and put it down again.
With vacuum operated petcocks, why do i even have gas flowing to the carbs with stopped engine? The petcocks are fine. Do i have a vacuum issue somewhere, on top of dysfunctional carbs floats/needles???
Temperatures are rising in Denmark and i want to hit the road, not the garage
I have searched this forum for help, but couldn't really find anyone with this particular issue.

[dpotter58]

The only way fuel will run out of the carbs is if the needles aren't seated. The vacuum opens the petcocks while the engine is running; it doesn't close them.
There may be some rust/dirt/ crap in the tank causing you issues with the needles. Another problem is some of the old floats leak and they fill with fuel so they wont float and shut of the needles. Pull them out and shake them. If you hear liquid they are bad.
Are your vent lines open? do you have the fuel lines running to the lower tees and not the vents?
good luck.

[Wolf]

I will adress all your remarks once i get the bike back from upholstering this week. Good info about the vacuum system, now it kinda makes sense. The vacuum from the running engine will force open the valve in the petcock. But shouldn't the flow from the petcock stop when the engine is turned off then, when the vacuum seizes? What else "closes" the petcocks?

[GLoweVA]

I will adress all your remarks once i get the bike back from upholstering this week. Good info about the vacuum system, now it kinda makes sense. The vacuum from the running engine will force open the valve in the petcock. But shouldn't the flow from the petcock stop when the engine is turned off then, when the vacuum seizes? What else "closes" the petcocks?

If they are stock petcocks, there's a spring in there that 'pushes' the plunger in there to shut off flow. some have rebuilt their petcocks with the wrong kits and the plunger isn't quite the right size, so maybe it's not sealing right.
An easy test is to have the tank off the bike (or at least disconnected fuel and vaccum lines) and see if fuel is still flowing thru the petcocks. (not on prime)

Secondly, the fuel should also stop at the carbs. The best way to set it up and test is with the carbs off the bike setting level, hook up a fuel source and fill the carbs. You can hook tubing to the bowl drains and use those as a level gauge to see what the height fo fuel is in the bowl. The key is to have them all the same height.
Like potter said, make sure your vent "T's" are free and clear and not capped.

[Wolf]

Thanks again
The petcocks have been replaced, so they are working just fine.
So the problem has to lie somewhere in the carbs. I'll have to take a closer look at these things once again and see if i can get the leak to stop.
One thing i apparently doesn't fully understand, is why gas is even entering the carbs with the engine off. To my understanding the flow should stop, kinda when you put your finger on top of a straw (if that makes sense )

[GLoweVA]

Alright, I'll post a hypothesis:
What if your compression is so good that when you shut the bike off, that the cylinder that the petcock is hooked to (has both valves shut) then could the cylinder 'hold' vaccum enough to keep the petcock open?

Just a crazy thought.

[CaptonZap]

When you say "the petcocks have been replaced", replaced with what? Used, new, rebuilt?
If the engine is off, and the fuel still flows out of 3&4, you have petcock issues. (They aren't shutting off).
Start there. Test them as GLoweVA suggested above.
And if the fuel quits flowing with the bike upright, look at the side play at the float hinges. It sounds like the floats are floating over to the side of the bowl, and as the fuel evaporates, they drop to let more gas in, and hang up on the side of the bowl or gasket.


CZ

[Wolf]

It sounds like i should check how the floats work at an angle. Sounds like a plausible solution. The petcocks have been replaced with refurbished ones, and they work fine. No gas flowing from the petcocks, it only happens when the bike has been running. I'll have to dig deeper into the problem before i can explain exactly when and what happens precisely.

[dpotter58]

Theoretically, it shouldn't matter if you have petcocks or not. If the floats and needle vales are working correctly they are what should shut of the gas flow.

[ViperRon]

The main cut off is the Float needles in the carbs. AS stated if float leaks, binds, or sticks they will leak. It does not take much to hang them open. Any trash, water, rust, scale, etc will hold the float needle open. I fi the gasket is not positioned correctly or has sweelled it can hang the float. The tang from the float can be bent or the float can be mispositioned slidding over or the tip of the float needle or the seat be worn and the needle will not allow the needle to settle every time. Tendancy is the float assembly will want to slide to the low side when idling and that can leave the needle slightly kinked over to the side where it does not seat.

The pitcocks if original need to be polished and re-serfaced if you put a new kit in. The metal tends to fatigue and you may not be tightening down good on the gaskets of the pitcock assembly. The oring seat assembly needs to be polished smooth and the gasket on the selection bar needs a smooth polished serface to mount and slide against. Also when assembling the assemblyits good to put a little lubricant on the seals when assembling.

Put filters on the line does not take much rust over a period of time for sediment to mess uo carb and use proper motorcycle gas line the regular automotive type has left rubber particals in carbs before.

The carb is your primary gas control and the pitcock is a secondary in the mantanance and repair sections of this site there are great pictures and write ups for exactly the areas to concentrate on.

I know I repeated what many above said but Clean Clean clean is the only way you find everything that causes issues. Dump and rinse works fine on a car will nor work here.

[DiverRay]

As an addition to ViperRon's post, check the floats with the carbs off the bike and upside down. I like to tilt the bank of carbs to the left and right, checking the floats VERY CAREFULLY to see that they do not bind on the side of the body or the gasket. When setting the float, make sure BOTH floats in each carb are CENTERED in their half of the chamber, and the same distance from the gasket surface. As stated, any slight drag will cause the floats to hang, and a fuel leak.

[natemoen]

Alright, I'll post a hypothesis:
What if your compression is so good that when you shut the bike off, that the cylinder that the petcock is hooked to (has both valves shut) then could the cylinder 'hold' vaccum enough to keep the petcock open?

Just a crazy thought.

Nope. The vacuum connections are in the carb intake boots which are essentially open to atmosphere. The butterflies don't seal well enough to cause a vacuum.

[motoman]

It sounds like i should check how the floats work at an angle. Sounds like a plausible solution. The petcocks have been replaced with refurbished ones, and they work fine. No gas flowing from the petcocks, it only happens when the bike has been running. I'll have to dig deeper into the problem before i can explain exactly when and what happens precisely.

Flip that carb bank upside down with bowls removed, hook up a fuel supply(tank set above carbs a couple feet), let it set for an hour looking for fuel weeping by the float needles.....easy-peesy. If no leaky, floats are hangin' on gasket edges or float is sinking (leaky float).....again, easy-peesy. No need to overthink it.

[Aches n Pains]

Ehat Motoman said. Simple place to start.

[Graman]

Gas pouring from carbs.

It sounds to me like your float bowl valves aren't closing. I haven't had this happen on my XS11 but it has happened on an old Honda Shadow that I am restoring. I solved mine with a whack from a screw driver handle but yours might be more serious. Pull the carbs and replace the float bowl valves. Make sure your floats are moving freely. Adjust them to the correct height. Did you replace the float bowl gaskets?