fuel out vent tube in prime

[chef1366]

Don't mess with the floats. Replace those o-rings. Get the kit from Robert Barr at Cycle O Rings Dot Com, and rebuild those puppies the right way. Even if they look ok, I guarantee you that those o-rings are trash at this point in time, if they're not been replaced. Imagine how you'd feel if you were dunked in gasoline for thirty some odd years. The problem gets worse each time you take them apart because those o-rings are tearing a little each time they get pulled. You might not be able to see the tears, but the fuel will find a way through.

Ditto
O-rings

[Colin Green]

The needle valve may have stuck open when you took them out. Try tapping on them with a screwdriver or something.

Does it flow out if the bike is off and the petcock is set to ON ? It shouldn't.

Basically, fuel will flow freely in the PRI position whether the bike running or not. The only thing ,at that point, to keep it from overflowing is the needle valve seats.

If you have fuel flowing in the PRI postion, you're supposed to. If it's overflowing, then you have issues with the needle valves.

If you have fuel flowing with the petcock in any other position with the bike NOT running, your petcock is done.

Don't mess with the floats. Replace those o-rings. Get the kit from Robert Barr at Cycle O Rings Dot Com, and rebuild those puppies the right way. Even if they look ok, I guarantee you that those o-rings are trash at this point in time, if they're not been replaced. Imagine how you'd feel if you were dunked in gasoline for thirty some odd years. The problem gets worse each time you take them apart because those o-rings are tearing a little each time they get pulled. You might not be able to see the tears, but the fuel will find a way through.

[Sandy]

Petcock is OK. It flows on prime, and doesn't when off prime. Good or bad though, the float needles are supposed to stop the gas. Maybe it's some crap in them from a dirty tank or as said just replace them and the orings. Oh yeah, if it's got brass floats maybe one of them is full of fuel and sank or maybe the float is binding or sticking when you put the bowl back on. Shake the carb, you should hear the float rattle. It shouldn't be that difficult to figure out ........famous last words.

[cowb0y]

Floats rattle and are integral (empty of fuel). O-rings makes sense from my experience and troubleshooting on these carbs. Got the O-rings on the way and will cautiously replace each upon arrival. I truly appreciate understanding the "why" of what I am doing.

[Larry D]

Floats rattle and are integral (empty of fuel). O-rings makes sense from my experience and troubleshooting on these carbs. Got the O-rings on the way and will cautiously replace each upon arrival. I truly appreciate understanding the "why" of what I am doing.

When you're sliding them back in the seats with the new orings, put a little spit on 'em so they will slide in easily. Be careful not to nick them.

[Steve]

All suggestions are good, so far, but I have a question of my own:

Fuel streams out the vent tube between carb one and two while petcock in "prime" and bike not running.

Why do you have the petcock in PRIme and the bike not running?

Yeah, I see where it happens when in the RUN position, too, but at least, when the bike is not running, the petcock will shut off the flow of fuel.

As mentioned (repeatedly), you have an issue with the float valves not sealing. You said the needles looked okay, but the needles are not the only sealing surface. The seats also need to be immaculately clean and it is so hard to see in there to check them. I just got new valves and seats from Parts-n-More for $8 each, so it's not all that expensive to change them. (Note that Parts-n-More has a $35 minimum, so you will need to find something else to buy, too. I got a new front brake switch for $6. )

One other item to check: are you measuring your float height at the correct location? You do not measure from the top of the float, you measure to the bottom of the step. This picture is not quite right, but you should have a better idea where to measure:


An actual float being measured:


.

[moose200]

what about the screw on the bottom? that happened to me, it was not tight enough and fuel started comeing out of the vent

[Steve]

what about the screw on the bottom? that happened to me, it was not tight enough and fuel started comeing out of the vent

Which "screw at the bottom"?

I have to ask, because depending on what bike you have, there is only one screw or two screws.

On the '80 and newer bikes with CV carbs, the only screw on the bottom is the drain screw for the float bowl. If that is not tight, yes, it will leak.
If you have a '79 or older bike with VM carbs, there is also a pilot fuel screw under the carb, but it should NOT be tight, it should be out 5/8 to 3/4 turn.

However, the "tightness" of either of those screws will NOT affect whether gas comes out the vents.

.

[Matchless]

Here is a little summary I made for someone a while back:
http://www.mediafire.com/file/0yucmnmwnjj/Needle and seat in BS34 CV and other carburettors.pdf

Maybe it will help you.

[GS1000S]

This may not be your problem but I had the inner rubber disc in my petcock, that controls fuel flow direction, start deteriorating after 30 years of use. It would shave a hardened piece of the disc about the size of a fleck of black pepper occasionally when switched to prime or between on and reserve and it would flow down and stick a needle valve open. Because it was on the downstream side of the tank standpipe filter it bypassed it. I tore my carbs apart 3 times before I finally found the small piece in the needle. When I disassembled the petcock I could see the area around one of the holes in the disc had been coming apart for some time.

[Mekanix]

I've had this problem for the past 3 weeks and finally fixed it.

Maybe this will help.

How can this happen?

1. If its the petcock or tank:

- Petcock diaphragm busted and fuel leaking into one cylinder ( the one your vacuum line is connected to)
- Tank is not venting and is pressurizing and forcing the gas past the needle and seats regardless of how well they seal.


2. Needle seats and needle/ Seat O-rings.

- Hard to tell if they are worn by sight unless its really obvious.
- O-rings will make them leak around the seats

- Setting the float height too high makes them top out and not close the needle valve
- Setting the float height too low makes them not have enough force to close the needle.
- worn needles and seats makes it harder to adjust the float level.


I fixed mine by looking at what it was actually doing with the float bowls off.

Took the float bowl off and set the petcock on prime, gas would flow until I pushed the floats high enough. Took that measurement and it was higher than the book specs so I set the float height again and again and still it would bypass the needle. but they looked great to the naked eye.

So replaced all needle, seats, and O-rings.

Problem solved regardless of what I set the float level too now.


P.S Avoid sandblasting a gas tank that isn't sealed perfectly :P

On mine, sand made it past the in-tank filter and the inline filter and the filter on the needle seat and ruined the needle seat.