Carbs leaking fuel when stopped

[nilsthenomad]

My '81 750K is randomly leaking fuel from the nipple at the base of my carburetors. I was riding yesterday and stopped for about 10 mins. When I got back to the bike I saw a puddle of gas and fuel leaking out of the bottom of carb #2. I figured it may be either the float needle or possibly the drain screw came loose, so I gave it a few taps with my screwdriver and loosened and re-tightened the drain screw and it stopped. Problem solved. Now today I drove about 3 miles, stopped for a few minutes and returned only to find that gas is now leaking from the bottom of carb #3. I repeated the task from yesterday and it stopped again, but have a feeling im just getting lucky and that something else is definitely causing this. I noted that whenever the engine was running the leaking never occurred. It was only while the bike was parked and off. I know there is just a good chance that something is gumming up the float needles and that I'll need to take em apart, but just wanted to check with everyone to see if there was a consensus. I had the carbs rebuilt by the dealership only about 1,500 miles ago, so am hoping that I don't need to do anything serious. Thanks for your help!

[Lucky 1]

It does not leak when it is running because it is burning the fuel at just enough of a rate to keep the float bowl from over filing.

i would order 4 new float needles with seats if thy are all metal.

it it has rubber tipped needles then just order the float needles.

Do not be tempted to rectify the problem by adjusting the floats.
It would just run poorly and still leak.

[shinyribs]

Lucky is right. It could also be a faulty float. Slowly absorbing fuel and causing the same symptoms. Yet when running it can consume the extra fuel it is allowing. Just like Lucky said.

[nilsthenomad]

Thanks for the advice Lucky and Shiny!

Opened up the carbs today and found some grime blocking one of the floats. Cleaned all 4 bowls out and it appears that the problem is solved. Everything moving great. The needles and jets are only 1500 miles old, so they were still bright and shiny. Phew. This however was my first time removing the carbs on my own, so upon re-installation I found that my throttle is pretty stiff and has no return. I obviously changed the settings of the cables somehow. I didn't move them much or change their path, so I imagine this has to do with the way I reconnected them. I'm still really new to motorcycle mechanics as a whole, so would love it if someone could explain the 3 cables that run into the carb bank and the best way to reset or configure them. As far as I can tell the forward most is the throttle return, the second one back is the throttle itself and I'm not sure about the one that runs into the back of the bank. I realize this is all pretty newbie stuff, but any explanation or system anyones got to their throttle setup would be great! Thanks!

[Piute]

                     Carbs leaking fuel when stopped
                                           
                                                     DON'T STOP
                     
                           RIDE-ON........

[Johnnylevi]

Hey nomad! So that first cable is the push cable which keeps the throttle from sticking. the second is the pull yeah and the back cable is the choke cable. To take those cables off i imagine you must have loosened some 10mm nuts where the cables sit at the carbs right? those are how you adjust your cables. You can download the FSM from the thread at the top of the home page. Which will tell you how much play the throttle should have.

[seestheday]

81 floats aren't adjustable anyways

[RodneyCB750K1979]

To prevent this from occurring again, you may want to clean/inspect the tank, replace fuel hoses, and install an in-line fuel filter. Fuel is not drawn from the tank bottom unless you are running on reserve.

[nilsthenomad]

Well, after a week of fiddling and fixing my carbs are spotless. My float needles only previously being barely used are clean (though they were almost spotless to begin with), my floats are empty and floating AND I replaced the bowl gaskets. Had a hell of a time getting a good vacuum with the 31-year-old boots, but softened them up with some tire foam and I now have a perfect seal. Put the tank back on, she started right up no vacuum leaks no gas leaks. Went for a quick 5 miles around the neighborhood, turned the engine off and carb #2 began leaking gas out the nipple again... Turned petcock to OFF and it stopped. Is it possible my SOS is just a POS?

[TOOLS1]

"Is it possible my SOS is just a POS"
YES!
TOOLS

[nilsthenomad]

Judging by the confidence in TOOLS' response, I'm guessing that if I remove the SOS, carb #2 will stop leaking and I'll just make solid use of my petcock?

[jbrightwell]

But even if the S.O.S is a P.O.S., the carb should still not leak .  There must be something else, correct?

[TOOLS1]

Yea. You still need to repair the problem with the carb overflowing.
TOOLS

[seestheday]

Yep. Did you check to make sure the tube in the bowl wasn't cracked? It shouldn't be given that you're having an intermittent problem, but you need to start eliminating everything.

Sent from my BlackBerry device

From: TOOLS1 [via Honda CB750'S]

Sent: Saturday, April 6, 2013 11:47 AM

To: seestheday

Subject: Re: Carbs leaking fuel when stopped

Yea. You still need to repair the problem with the carb overflowing.
TOOLS

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[seestheday]

One other thing, are you running a fuel filter? Crap from your tank could be clogging it again, after you cleaned them.

[dantmcclellan]

So, my carbs are also leaking. I took 3 of the 4 bowls off though & everything was squeaky clean & seemed to be working fine (stopped the fuel when I pushed the float up by hand)

Is there any other problem that could cause this?

For clarity:

needles looked new (rubber tipped)
floats had no holes or any visible damage
floats pivoted freely on the hinge

I have no idea why it still drips sometimes.

[TOOLS1]

Heavy/deteriorated floats. You might try setting them lower.
TOOLS

[kandrtech]

I've seen carb bowl overflow pipes with cracks....

[Re-run]

Does it still drip while riding? I know a lot of people, not just with CBs, that will turn the petcock off while parked as long as things don't drip while riding.

Otherwise, some baking soda with a little water to form a paste, use a q-tip and work at the needle seat, kinda like lapping a valve.

The baking soda grit will usually take off most crud while doing no damage to the metal itself.

After that, use a cup of gas and place each float in it and see how well they actually float.

Next test would be to set up each fuel bowl and put gas in them and let them sit. Fuel bowls can leak from 2 places, the drain tube having cracks, or the drain screw not sealing.

Just be careful since you are using gas. I would suggest water but water isn't thin like gas is.

If you have the seats clean, the floats actually float, and the bowls do not leak, assemble everything and check float height.

Find the height for your bike, since you didn't list it, I don't know what you need. Hold the carbs so that the floats close the needle but do NOT push in the little pin in the middle of the needle, usually about a 45 degree Angle or so. Measure the float right at its middle. For example, my floats at 14.5mm +- .5mm, so I need to be between 14 and 15 mm.

If you need to adjust height, bend the tab that the needle hooks to the float on till it is in the proper range.

Once float height is good, put it together and see what happens. One thing is to check the needle tips since they are rubber. They should be slightly soft, it is thin rubber so not much give. Deep rings in the rubber could mean they are worn out.