Fuel leaking from the carbs

Hi everyone,
Ive got a 1989 KZ650 SR. Ive been rebuilding that thing for months now just getting everything working properly. This problem just came up the other day though. One of my carbs is leaking fuel from the tube underneath the bowl. These are Mikuni carbs and not the CV ones. The all have a screw in them that will drain the bowl but then they also have another tube coming out the bottom. Overflow i guess? Anyways, my petcock is not working proporly and is always leaking gas out of it no matter what position its in. It used to not be such a worry to me but now that the carb is leaking fuel, it is a problem. Its just the number 3 carb doing it. While the bike is off, maybe every 30 seconds a couple tablespoons of fuel will squirt out of that little tube. Not sure why. I took them apart and cleaned the heck out of all of them. Now im not sure what the issue is. Maybe a bad float but i just wanted to see if there was anything else i should check....Thanks a ton in advance everyone!

Regarding the carb overflow -

Fuel coming out of the overflow hose (the little hose on the bottom of the carb) is the common symptom of the 3 possible problems described below. Remember - NO SMOKING or other activities that could ignite the fuel while working on carbs!

The float valve is not sealing. This may be (and probably is) just a matter of some minor dirt in the float valve and is very simple to remedy and can be done with the carbs still on the bike. Turn off fuel; drain carb by loosening big brass screw near bottom; and remove the 4 little screws on the bottom of the carb bowl. This will enable you to remove the carb bowl. You will then see the float. If you carefully remove the float you will see a stubby little needle that mates with a brass orifice; together, these two pieces are the float valve. Assuming there is no obvious damage to the needle or seat, use a Q-tip and some carb cleaner to clean the seat of the orifice and the needle. Be careful not to bend the tang that is attached to the float. This tang is the piece that the bottom of the float valve needle rests upon, and it determines the fuel level in the bowl, so bending it will change the fuel level. With the float valve cleaned it should no longer leak. To prevent a re-occurrence a quality inline fuel filter should be installed between the fuel tank and carbs. If there was damage the needle and seat should be replaced as a set; they are available.

The brass overflow tube inside the carb bowl is damaged. When you remove the carb bowl you will see a brass tube attached inside and rising toward the top of the bowl. This is the overflow tube and it leads directly to the overflow nipple on the bottom of the carb. Normally, the fuel level within the bowl rises somewhat close to the top of this tube. If the tube becomes cracked or separates from the bottom of the carb bowl fuel will flow through it and out through the overflow hose. Checking the condition of the tube is very easy after you have removed the carb bowl from the carb. Simply hold the bowl level and fill it up near the top of the tube with water or alcohol and see if it leaks. A slight crack in the brass overflow tube can be difficult to find. You can connect a rubber tube to the overflow nipple, fill the bowl with water, put finger over the open end of the brass overflow tube and blow in the rubber end and look for bubbles. If it does the best remedy is to replace it although some folks have found creative ways to repair them.

The fuel level is set too high. This condition occurs when someone has bent the float tang as mentioned above. This condition can be checked using what is referred to as the "clear tube test." The test involves attaching one end of a clear piece of flexible tubing to the carb drain hole and holding the other end of the tube above the bowl/carb joint. When the fuel is turned on it should rise in the tube to a level 2.5 - 4.5 mm below the bowl/carb joint. If the fuel rises higher than that level it may run into the cylinders or over the upper end of the brass overflow inside the carb bowl (mentioned above) in which case it will run out the overflow hose. This condition is corrected by removing the float and gently bending the tang to raise the float valve needle position. Doing this may take several tries before achieving the desired fuel level.

Correcting each of these three conditions involves removing the carb bowl. This task can be made easier if a short screwdriver bit is used, and depending on which carb you are fixing a mirror may help you locate the screws on the bottom of the carb bowl. Also, it is not a bad idea to have a new carb bowl gasket available in case the old gasket is damaged while removing the carb bowl. Ed

danoid, I'm uncertain if you resolved the issue with your overflowing #3 carb?

I had a similar issue with carb #2 when I was getting the engine on my 650 project bike to fire the first few times. Gas would spray about every minute from the overflow tube. You also mentioned a petcock problem.

First, make sure you have enough gas in the tank, 2 gallons minimum in order to avoid running on reserve, DO NOT RUN ON PRIME.

Remove, disassemble the petcock, clean, check and put it all back together. My 79 650 petcock isn't gravity fed and has an air tube connected to it. If it's not all clean and functional (good seals all around), it will cause problems.

And check everything 650ed just mentioned (above).

...just my 79 cents.

I noticed this thread and I would like to add some questions of my own in here as well.
I have a 82 CSR the big twin. My Petcock is also acting funny and allowing fuel to flow all the time. When the motor is running and shortly after turning off nothing leaks and the bike runs good. After about 10-15 min of being off the carbs will leak out the air intake I'm assuming after the bowl fills and fuel keeps coming.
I got the Petcock rebuilt kit and replaced all the seal except the vacuum seal. I noticed the previous owner "Shoe49" I believe had that sealed with cork gasket and the vacuum tube disconnected and plugged. Since I was not sure why this was done I have left that as is for now.
Does anyone know why this would be removed and sealed off like this???
I am contemplating putting it back but would like some feedback

You have multiple problems.

First - assuming you are not leaving the petcock turned to the "Prime" position it needs to be rebuilt or replaced. It should stop the flow of fuel when the engine is shut off.

Second, the carbs should not be overflowing no matter how poorly the petcock is working. See my posting above regarding carb overflow. Ed

Marine5954 wrote: ... After about 10-15 min of being off the carbs will leak out the air intake I'm assuming after the bowl fills and fuel keeps coming.
I got the Petcock rebuilt kit and replaced all the seal except the vacuum seal. I noticed the previous owner "Shoe49" I believe had that sealed with cork gasket and the vacuum tube disconnected and plugged. Since I was not sure why this was done I have left that as is for now.
Does anyone know why this would be removed and sealed off like this???
I am contemplating putting it back but would like some feedback

Where fuel has leaked out the air intake, it may have also entered the crankcase.
Would sniff-test and examine the oil to determine whether there's fuel contamination, and if so would disconnect the fuel line from the carb and change the oil and filter and not allow any fuel to enter the carbs until the overflow issue is resolved.

Good Fortune!