Leaky carb

[Audioslave784]

This past weekend I cleaned my carbs and put them put them back on the bike. The next morning I noticed that carb #1 was leaking some gas. I opened up the float bowl on the bike, raised the floaters manually to try and unstick the the needle, then put the carbs back on. The problem went away.

Last night I took the bike for a ride, and everything felt okay. Then this afternoon I check on the bike and carb #1 is leaking again.

I know, my petcock is shot. But what I'm confused about it what happened today.

I just took off the float bowl again, and found that if I raise the float manually even just a little bit, the pin is depressed and the leak stops completely. However if I just put the float bowl back on, the bowl fills right up and overflows like crazy. It's almost as if the floaters are not floating at all.

The bike is currently sitting with the float bowl off, and with a piece of metal holding the floaters up so cut off the gas. There is no leakage whatsoever.

What could be happening here? Is it possible that the floaters could have developed a leak and filled with gasoline? They don't feel particularly heavy...

[almarconi]

Drop the "floaters" in a cup of gas and see if they float.

[tkent02]

You are trying to use the floats to do the job of the petcock. Fix the petcock. Adjust the floats correctly. Make sure they float.

[Matchless]

The main cause of "leaking" carbs as you put it is the failure of the needle and seat to block the fuel flow and many times this is caused by dirt or by someone who removed the seats incorrectly to clean the mesh or replace the o-rings. If the brass seat is gripped with a pliers the open end is slightly ovalled and can cause the needle to stick open or closed in certain positions. It will not always happen as it is triangular.

The petcock cutoff is an excellent method of providing backup for the fuel flow cutoff and should not be replaced with a standard on/off type even if it sounds very cool! You WILL forget or someone else will and you will get fuel mixed with your oil!
The bike is not supposed to be ridden while the petcock is on prime, as you are overriding that fuel cutoff feature, but it should be possible to leave a bike on prime or drive it on prime without the carbs overflowing at any time.

The needle and seat should also cut off the fuel flow if the filling of the bowl is happening faster than what you are using fuel, thus over flowing while the motor is running and causing overfueling problems. In such a case even a good petcock will not help much.

Check, clean and repair or replace your needle and seat as this is the only option and the correct way to go!
In addition make sure your "On" position of the petcock only flows fuel while the engine is running and cuts off properly while not.

Hope this helps.

[BassCliff]

Hi,

I saved a few words of wisdom from one of our resident gurus on my website. I'll share them with you...

Overflowing Carbs by Mr. bwringer

Let me point out the obvious: If a carb (or carbs) are overflowing when the bike is not running, you have TWO problems. First, your petcock should prevent ANY flow; second, the needle valve should allow flow only up to a fixed height in the bowl (ie, not overflow). Excess fuel has to make its way past both of these parts.

(A third possibility on old carbs is for fuel to flow past the inlet seat O-ring. [n/a for VM]. That doesn't apply to newly rebuilt carbs, since the owner has just installed brand new. Right??)

I'm not 100% sure why some needle valves leak and others don't, but I'm starting to lean with Keith Kraus' suggestion, which is to use only OEM valves and seats. Simply because it works. The question why is a separate matter. (I have a theory, but no guinea pig to test it on at present).

For the petcock, you'll hear a number of suggestions. I think that the vacuum operated petcock should be kept operational, for a few safety reasons.

Several of the folks here are convinced that petcock rebuild kits are useless, and your only real option is to buy a new OEM petcock.

For now, for people who are 100% sick of carb overflow & the ensuing problems, the consensus then is to go with OEM petcock, seats & needles. it's expensive, but it seems to be the only certain way to correct this BS once and for all.

(I would add: no doubt there are people whose overflow problems began when they installed carb rebuild kit(s). The machining on the parts is often abhorrent and inexcusably amateurish, and the f&^%#ing O-rings don't fit correctly. The consensus for a while now has been to buy gaskets IF you need them, valve seats & needles IF you need them, and an O-ring kit.)


The petcock does not, in any way, REGULATE the rate of flow. It should be either on or off. If you have overflow on a running bike (and it's not inhaling fuel through the petcock diaphragm via the petcock vacuum line) then there's a problem with the inlet valve.

Either:

1) the float is no longer buoyant enough or is badly adjusted, or

2)the valve is bad, or is being held open by some foreign matter.


Thank you for your indulgence,

BassCliff

[Nessism]

One thing to check is to make sure the float is not bent and hitting the side of the floatbowl thus keeping it from moving freely. Another thing is to check the small float valve seat keeper tap, it keeps the floats from moving too low and binding. These tabs are often bent which will allow the float to move down too far - a position from often they get stuck.

[Audioslave784]

Thanks for the tips guys. I'm really not looking forward to getting that float pin out, but I guess it's got to be done, and anyway it looks like there's a lot of good advice on the GSR on getting them out without breaking the posts.

The plan now is to check the following:

1. Float valve seat keeper tap bent?

2. Floaters bent?

3. Floater buoyancy

4. Valve and seal

5. Buy a new damn petcock from z1

Not sure if I can get to it this weekend, but when I do I'll let you guys know how it goes.

[Nessism]

Sorry to sound harsh but how can you "clean" your carbs if you never took the float needle out? If you live on So Calif I'm going to come over to your place and slap you upside da head.

It's time to do a hard stop and perform a complete carb rebuild. Do not pass go, do not collect $200. Go straight to jail and don't come out until you clean the carbs properly and replace all the O-rings with a kit from cycleorings.com. The 30 year old o-rings in your carbs are hard and brittle, time to change them unless it's been done recently.

You just proved that short cuts are long cuts when it comes to cleaning carbs. Sorry for the public flogging but please treat your GS right. We love our GS's around here and it upsets me to see one abused.

[rustybronco]

This is one more reason, that I have been suggesting you check the "wet" fuel levels on the bench, before re-installing your carburetors.

[Guest]

Whack em with a hammer. Seems to work for many.

[Nessism]

This is one more reason, that I have been suggesting you check the "wet" fuel levels on the bench, before re-installing your carburetors.

Good suggestion here.

I made a couple of fuel level gauges by drilling some old floatbowl screws and gluing a piece of copper tubing to the head with JB Weld -attach clear tubing to the copper to complete the gauge.

I bench tested the carbs for my 1000 and was stunned by how sensitive the float adjustment is; just a small tweak of the float height caused a very noticeable change in the fuel level in the carbs. I'd go so far as to say that the float height has to be almost exactly right at the nominal spec in order to get the fuel level in spec. If the float is adjusted toward the edge of the tolerance range, the fuel level will be out of spec.

[tkent02]

Good suggestion here.




I bench tested the carbs for my 1000 and was stunned by how sensitive the float adjustment is; just a small tweak of the float height caused a very noticeable change in the fuel level in the carbs. I'd go so far as to say that the float height has to be almost exactly right at the nominal spec in order to get the fuel level in spec. If the float is adjusted toward the edge of the tolerance range, the fuel level will be out of spec.

Have you checked fuel levels on a bench and again with the engine running?
I'm curious if they would be the same, I would guess not quite. But I've only ever checked them on a running engine.

To bench test it, what do you do, just let the bowls fill and see where the level is when it stops?
Or is fuel flowing somehow and you are reading the level as it flows?

[rustybronco]

Have you checked fuel levels on a bench and again with the engine running?
I'm curious if they would be the same, I would guess not quite. But I've only ever checked them on a running engine.

To bench test it, what do you do, just let the bowls fill and see where the level is when it stops?
Or is fuel flowing somehow and you are reading the level as it flows?

Tkent02, I have checked the "wet" levels on the bench, with the carbs orientated like they are when installed on the bike (it was on a xv920j). then re-checked with the bike running; there was very little difference.

the way I use to bench check them is, with a funnel stuck in a fuel line and held about two feet above the carbs. that way there is some "head" pressure, approximating the height of the fuel in a fuel tank.

[tkent02]

the way I use to bench check them is, with a funnel stuck in a fuel line and held about two feet above the carbs. that way there is some "head" pressure, approximating the height of the fuel in a fuel tank.

So let the bowls fill and see where it stops?

[rustybronco]

So let the bowls fill and see where it stops?

Yes... then "tap" the fuel bowl(s) to remove the bubbles in the clear line.