Reading This May Solve Your Leaking Carburetor Float Needle Valve And Seat Problems

[greaseyfingers]

A Remedy For Stopping A Leaking Carburetor Float Needle Valve And Seat, on my 76 Kawasaki KZ 900 and 79 Kawasaki KZ 1000 ST.
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Do you know what causes gasoline to drip out of the over flow drain tube of your carburetor?

The short answer is that a tiny piece of dirt is, most likely, stuck in the needle and seat of the float valve, preventing the valve from fully seating. Or else your float valve may need to re-adjusted to obtain a correct fuel level in your carburetor's float bowl. Or if your if your carburetor's needle valve and seat are excessively worn, they may start leaking and need to be replaced.

However, I'd like to give you a bit more background on this important question. I used to think that the float valve in the carburetor operated like the float valve in the tank of a toilet: i.e., when water in the tank got low (as in after flushing), the valve would open until the tank filled and then close again. However, it is important to realize that (unlike our toilet tanks) the needle in the carburetor float valve is always closed, while the fuel level in the float bowl is being maintained. What varies is the pressure that the carburetor float exerts on the needle: relatively high as the fuel level increases, and relatively low as the fuel level decreases.

This means that the fuel pressure (on the inlet side of the valve) is working in constant equilibrium, as it's equalizing with the pressure exerted by the float valve needle (on the carburetor side of the valve), so that a very constant level is maintained in the float chamber.

Understanding that the needle of the float valve is always being pressed against the seat is important in understanding why any tiny bit of dirt can cause so much trouble. Once a piece of dirt gets caught between the needle and the seat, it will be held there and interfere with the needle valve's ability to control the fuel level, until such time as fuel is drained from the carburetor and the piece of dirt is flushed away. This is the reason for the flushing procedure of the fuel system, by removing the drain plug from the bottom of the float bowl and let enough fuel run out. Which will usually rinse off the the debris that is on the needle valve and seat, providing the debris is small enough to go through the needle valve seat orifice, as the fuel is draining out of the float bowl drain screw hole.

To help prevent this problem from happening, again. It's advisable to put a good reliable inline fuel filter between your gas tank and carburetors to keep your fuel system as clean as possible that's going to your carburetor's float valve and seat. Which will, also, prevent other problems from occurring in your carburetor, too, from dirty fuel.

In addition to dirt causing the valves to stick open, I have seen a few cases where the brass seat of the float valve needs to be polished (smoothed out) by pressing and rotating a short, sharply pointed hardwood dowel into its small orifice. Dowels of 3/16” diameter work well. I have even had to clean up brand new seats in this fashion before they would stop leaking.

[Nate]

That makes sense. It's common to think of an opening and closing valve, but the near constant pressure works because gas doesn't need much of an opening to flow.

Even with a filter a rusty/dirty tank will cause frustration to no end until the rust is neutralized and the tank is sealed or treated to prevent the rust from recurring. I now understand better why the filter doesn't eliminate the problems.

[workingtoride]

i to have the fuel leaking out of the drain hose (78 kz650B)so i first took the lines off the petcock and no fuel leaked out, i drained all 4 carbs by removeing drain screw completly onto papertowel and some dirt did come, so my ? is after the 1st big part of the fuel drained out the still seamed to have a endless amont of a trickle come out how is this possible if the bike is not running? I dont know alot about the carbs and set-ups - this is 1st bike and know i need them rebuilt - will have it done when the snow flies.. thanks

[tomz83]

Excellent info! Thanks!

[snardle]

Gas leaking while not running could be o_rings on the drain screws.

[Nate]

Originally Posted by snardle

Gas leaking while not running could be o_rings on the drain screws.

After pondering this for a bit, I think that would be possible but only if the outside of the carb bowls are damp and dripping onto the engine case. If fuel is coming out of the overflow hoses than either the float is unable to stop the fuel flow due to debris as described by the OP or the float level is incorrect and allowing the bowl to overfill. A third possibility is a bad float, but that is rare compared to the other two issues.

[workingtoride]

i had the drain plug all the way off the bike - so the float being stuck open will let gas come from the tank? i do know the carbs need done the bike sat about 5 years in a shed. i guess i need to read some more on the way the carbs work i dont see if you need a vacum to draw the fuel out when its running why it will leak when it is not since none came out of petcock when i took off lines - and out side of carbs are dry. so i guess back to more reading and get the carbs done. -----------would the float level change do to sitting all that time? boy so many ???? thanks for the info - hopefully one day it will all click!!

[antiq]

Originally Posted by workingtoride

i had the drain plug all the way off the bike - so the float being stuck open will let gas come from the tank? i do know the carbs need done the bike sat about 5 years in a shed. i guess i need to read some more on the way the carbs work i dont see if you need a vacum to draw the fuel out when its running why it will leak when it is not since none came out of petcock when i took off lines - and out side of carbs are dry. so i guess back to more reading and get the carbs done. -----------would the float level change do to sitting all that time? boy so many ???? thanks for the info - hopefully one day it will all click!!

In your case I think the answer to your question is the petcock is letting a little by and may need cleaned, rebuilt or replaced.

[Circe]

I recently opened up and cleaned out my carburetor. Now I find that when the engine is stopped an amount of fuel (maybe half a shot-glass worth) leaks out of the carbs somewhere. Do you think that what you describe with the floats is what my problem is, or is it possible that I didn't screw on the bowls tight enough when I put them back in?

[coppertales]

is the oring on the float valve body being old and not sealing properly. Being the cheapskate I am, I pull the valve body out and apply a thin coat of copper sealant to the body/oring and reinstall. This has worked for me for years. That sealant removes easy when/if you get new orings. Otherwise, pay the dealer for the orings to do the job right.....while you are doing this, check the float height setting to make sure it is correct.....chris3

[Circe]

I'll try getting that sealant and splooging up my o-rings. I'm getting sick of the fuel running out of the carbs and having to crank the engine until the battery runs down. I'll let you know how it goes.

[kzbatbike]

I like that dowel idea. Thanks

[greaseyfingers]

Originally Posted by kzbatbike

I like that dowel idea. Thanks

your welcome..

using a pointed short pointed 3/16" hard dowel, by pressing and rotating into the small orifice of a motorcycle's brass float valve needle seat, works wonders to polish and smooth it out, for obtaining a leak-proof needle valve seal into the brass float valve seat, so it won't leak, when all else fails, as long as the needle valve and seat aren't, already, worn out from excessive wear.. good luck..

In addition to dirt causing the valves to stick open, I have seen a few cases where the brass seat of the float valve needs to be polished (smoothed out) by pressing and rotating a short pointed hardwood dowel into its small orifice. Dowels of 3/16” diameter work well. I have even had to clean up brand new seats in this fashion before they would stop leaking.

[Circe]

The idea of greasing the o-ring solved my problem. My bike now starts on a dime. Thanks, and +300 to you. I wasn't sure what you mean by "copper sealant", so I got waterproof o-ring grease, which works great.

[coppertales]

It is silicone based so It comes off easy. Glad the tip helped.....I am going to make up a dowel tool now....chris3

[ratvespa]

one other thing you can do to "re-seat" the float valve is get some fine valve grinding compound, dip the tip of the needle in, then stick it in the needle seat and spin it round and round.

note, this only works when it's a brass needle.

[new rider girl]

I left the gas valve open on my bike and found i have gas going into my spark plugs and someone told me to come to this form said I may get some help i took the plugs out and let it air out for about five days i know along time but could not get back to it until today and i changed my oil due to the gas getting in it and replace my plugs my bike still would not start so I took the plugs back out and they smelled of gas again and when I turned the bike over gas came out of the plug holes this is my first bike and i would like to ride it soon how do I find the float valve to see if that is the problem

[zoro]

Originally Posted by new rider girl

I left the gas valve open on my bike and found i have gas going into my spark plugs and someone told me to come to this form said I may get some help i took the plugs out and let it air out for about five days i know along time but could not get back to it until today and i changed my oil due to the gas getting in it and replace my plugs my bike still would not start so I took the plugs back out and they smelled of gas again and when I turned the bike over gas came out of the plug holes this is my first bike and i would like to ride it soon how do I find the float valve to see if that is the problem

Hello NRG,First off,lets get some details and history of the bike,oh,Welcome to the Forum and the "Vintage"section! Alot of old riders on old bikes hang out here sharing several hundred years of combined experience and knowledge,"cant buy that"!Now then,details and history!Miles on the bike?How many owners before you?Was it running good when you got it?Do you have a "SERVICE"manual specifically for that bike(model and year)?If not,get one! Not an owners manual,a SERVICE manual!Sounds like you dont mind getting your hands dirty and thats a good thing!Drain the oil out of the bike into a clean pan and measure the amount drained along with a sniff to see if gas has entered the crankcase.There is no dipstick on these bikes,only sight windows and careful measurements when adding oil.The amount of oil that engine requires should be cast or stamped on the filler cap or on the case near the cap.We need this info to begin narrowing down and identifying the problem(s).OK? You are about to get very acquainted with that bike,Its going to make a better rider out of you,... if it dont hurt you first! Still in?....come on with that info then! Oh yeah, dont run that bike until you know for sure no oil has entered the crankcase Let us know whats up,youve been adopted "Alright Then"

[new rider girl]

the bike had One owner before me and left it in the shop until I bought it it is a 2003 with 201 miles on it it is a 250 exf ninja i will have to find a service manual for the bike maybe I can find one on line the bike ran great when I first bought it but I laid it down about two weeks ago on the highway doing 55 bike got a little banged up and i got alot of road rash but other wise the bike still started right up after the accident i just redrained the oil and replaced the plugs and the bike started up but I will rechange the oil before I ride the bike my cap on the oil says 1.9 for oil so if I put close to 2 in would that be about right i am not afraid to get my hands dirty and have done most of all this work myself had to take the radiator off and have it fixed then put it back on myself I will check to see about the oil tomorrow due to having to go to work in a little bit but I want you to know I appreciate all the help I can get and I go take the riders saftey class this weekend due to no license for it ya I know but could not risist riding it on that pretty day should have say my butt at home but don't cry over spilt milk to late for should have dones now I just want my bike in the best condition i can get it in again thank you

[07Ninja250]

My bike runs fine, with the exception of some decel popping, which I'm still chasing.

But I did have something strange happen one day while trying to synch the carbs.
With the bike not running, I took the tank off and ran some fuel lines from the tank (sitting on the work bench) to the carb lines. Petcock set to "ON". One fuel line, one vacuum line.

Out of curiosity, I removed the fuel tubing from the petcock and held it up, and watched the fuel slowly drain down the tubing and into the carb. It just kept going and going. I thought the float valves would eventually stop it, but it just kept going. I added fuel to the line, and that too flowed right into the carb.

I guess I don't have overflows on these carbs, because all that gas ended up in my crankcase.

I don't get fuel in the crankcase with the bike assembled like normal (tank on, normal fuel lines connected). But any additional fuel pressure coming into the carb (from a long section of tubing, full of fuel, held up) apparently makes its way right past the float valves.

I had to dump a pan full of brand new Mobil 1 because of this.

Is this normal, or do I need to install new float valves? I can only assume that if they get any worse, they'll start allowing too much gas into the carb at all times.

Any thoughts? '96 Yamaha Virago 750