Another Carb Fuel Leak. Please HELP!!!!

[flyanimator]

I have a 1980 GS1100 LT with the factory Mikuni BS34SS carbs and I am having a fuel leak problem that i cannot seem to figure out. I hope some of the many knowledgable folks on this forum can help me figure this out so I can get her back on the road.

The Issue
Fuel leaks out of the main air jets on the 2 right carbs (i guess #3 and 4) as well as the overflow drain "T" that these two carbs share. The carbs have been cleaned (dipped) and the float height has been set to the factory specs as per the manual (24.4 mm). I also tested the floats for buoyancy, and they all performed the same. I set up a fuel resivoir to test the carbs for leaks on the bench before putting them back on the bike (since i was getting tired of putting them back on and taking them off several times) and the previously stated leaks were found.

Just some history of what's been done to the bike
Before the carbs were cleaned I had sent them to get rebuilt by a local shop since I had just purchased it and it had been sitting for a while. When I got the bike back it ran ok, but I notice it was running super rich, like getting a miserable 12 MPG rich!!! I decided to jump into it myself since the shop did not really inspire confidence in me. Sure enought the floats were set way low. I set them back to spec and the bike really responded to it, ran better and didn't bog down when I opened the throttle. During that time I also adjusted the valve clearances. It should be noted that before I worked on the carbs myself, it did not leak. After working on them is when the leaks started (all four carbs) though I fixed the leaks in the #1 and 2 carbs quickly (float was getting stuck, tapped on the bowls and it fixed the problem.)

Other Modifications
After getting the bike back from the shop for getting the carbs cleaned and before working on the carbs myself, the ignitor box went out so I decided to install a dyna S ignition and replaced the coils with the ACCEL high performance coils. Not sure if this information is relevant, but just in case.

I hope someone can chime in and help me out with my first bike. I've been using the search function for the past several days but have not been able to find help for the issue that I seem to be experiencing. Thank you in advance for all of your advice.

[BassCliff]

Hi,

Here is some wisdom I've collected from Mr. bwringer....

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.

And finally is the standard BWRINGER's lecture:

One of the secrets of the GS850 engine and carburetion is its outstanding low-speed manners. This, in turn, allows you to much more easily exploit the corners of its handling envelope, which leads to more giddy fun than you've ever had with your clothes on. As most racers eventually find out, smooth is fast.

If you had a freer-flowing aftermarket exhaust, a good set of K&N pods, a dynamometer, exhaust gas analyzers, a degree in chemical engineering, no neighbors to bother, a few weeks off work, a large box of Keihin jets, and several fifths of good tequila so you can sleep at night, you might be able to extract a few more horsepower from the 850 engine at certain RPM. And if you're really good, you might be able to get the low end half as smooth as it was stock. Maybe.

With the stock exhaust, forget it -- all you're going to do is screw up everything else quite badly to get maybe 5 more horsepower at 7,500 rpm or something like that. These things have a certain balance, and more intake flow must be balanced by more exhaust flow.

Thank you for your indulgence,

BassCliff

[rideOn]

i can't add much. i had overflowing when i first got it. i adjusted the floats.

[Dave8338]

Have a look:

http://www.thegsresources.com/_forum/showthread.php?t=151724

[chef1366]

The main jet is connected to the main air jet. The only way fuel can get there is through the main jet. This means the bowls are filling over that level and forcing it's way out the air jet.
Either the o-ring on the float inlet valve is bad or the float heigth is off. It could also be a bad petcock along with a leaky float seat and needle.
Not that many variables.

[flyanimator]

Thank you everyone for your helpful advice. Where can I purchase one of these o-ring sets since I cannot seem to find them on the websites I buy parts from? Also, I know it was mentioned that OEM seats and valves are best. How can I make sure I'm getting OEM though? I have seen some carb rebuild kits with gasket, a coupe of o-rings, jets, seats and valves for about $23.00 but I don't know if they are OEM or at least OEM quality.

Can I get just the two seats and valves that are leaking or should I replace all four? Also I have seen on Z1 that they have just the needles for a few dollars. Could I get away with only replacing the needles and not the seats? Sorry for all the questions, and trying to "fix" the issue as inexpensively as possible. I'm a college student and disposable income is extremely limited.

Thank you once again for all of your help.

[chef1366]

I have some good needle and seats.

http://www.cycleorings.com/

Before replacing the needle and seats try the o-rings.

[Matchless]

Just a comment, if the o-rings on the needle seats are new and the needle tips do not show any wear then check that all four are in the same condition. If one is more worn than another and the needles were removed and not installed in the same seat then you may have leaking problems after working on the carbs. In such a case you would be better off replacing all four.

Secondly if the seats initially were stuck and pullled out using a pair of pliers then the possibility exists that the open end of the seat may have been slightly distorted, causing the needle to stick in certain positions. A new 5.2mm drill bit is a usefull measuring tool here.

To test the float valve working, set the bank of carbs up horizontally and connect a funnel to the fuel inlet, fill up until the funnel is halfway full, mark the level and leave it for an hour or more. If the level dropped then feel the throat of the carbs and the wet one will be overflowing, check that needle and seat out.

[flyanimator]

Thnk you Chef. How much are you asking for the valves and seats?

[pakulap]

I too had that 12mpg problem, but after the $150 carb rebuild kit investment.
The petcock rebuild fixed the prime to on problem, but still leaking until I siliconed the bolts heads.
The gasket washers were either gone or worn out.
Hope this works on the first nice day in January.

[ryder60]

I had a problem similar to this but it didn't show up until I had been riding the bike for a few miles. I did the carb settings thing and it didn't fix the problem. I went to the local tech, who is a GS affectianato and he threw the floats in a container of gas and they all floated well but 20 minutes later one was at the bottom. I like Matchless' technique of supplying fuel and waiting an hour to see if a float wasn't the problem.

[Nessism]

You guys with overflowing carbs might want to make a fuel height gauge. They are easy to make by drilling a hole into an old drain screw and then epoxying a piece of tubing into the hole, to which a piece of clear tubing is attached. The factory service manual shows these gauges being used – it’s pretty easy and will tell you definitively if the fuel level is in spec. Also, using a piece of clear tubing on your vacuum line to the petcock will tell you if gas is flowing into the engine that way.

[bwringer]

I'll reiterate something above, and state that it's fairly common to rip one or more of the o-rings around the needle seat upon installation. Especially if you tried to use o-rings from a rebuild kit -- the kits are well-known to be nothing but shoddy junk.

DAMHIK.

Fortunately, a complete set of the correct o-rings is cheep n' E-Z to get: http://cycleorings.com




Also, I might have missed it, but is the petcock a brand new OEM part? Old petcocks have mung inside, and when you move the petcock lever, or just try and use the petcock normally, bits of this evil mung can travel unimpeded to the float valves and prop them open at inconvenient times.

[flyanimator]

Update

I got my o rings in the mail yesterday so I'll be working those in later today after my exams are over .

For those who have asked about the petcock, it's not an issue at this point. I will be replacing it soon, but the carbs have been leaking when I bench test them while using a seperate fuel reservoir suspended above the carbs (i used an inline filter just to be on the safe side.)

Chef: Any word on those needle valves? Please let me know. Thanks .

[Steve]

... the carbs have been leaking when I bench test them while using a seperate fuel reservoir suspended above the carbs ...

How high above the carbs?

You need to somewhat duplicate the conditions found while riding and keep the fuel level no more than about one foot higher than the carbs.
If you go much higher than that, then the additional pressure caused by head height will be enough to overcome a float valve.

.