Does the overflow stop on its own after a while, or does it continue until you set the bike on the centerstand? Here's why I ask - assuming your petcock is the stock vacuum operated type, and assuming you do not leave it in the Prime or Reserve position, the fuel flow from the tank to the carbs should stop as soon as the engine is shut off. If the petcock is operating properly, any leakage from the carbs should stop after a while becasue there will be no fuel flowing from the tank to replenish the carbs and allow them to continue to leak. SO, if the carbs do not stop leaking after a while you cave 2 problems - 1 problem with the carbs and 1 problem with the petcock.
If the fuel flow does not stop after a while, the petcock problem must be addressed. It is possible that the diaphragm is damaged and permitting fuel to flow through the normal fuel line. This can be easily checked by removing the fuel supply line from the petcock (with the petcock in the RUN position and the engine OFF) and checking to see if any fuel is coming from the line. There should not be any fuel flowing through that line under those conditions. It is also possible that the damage is permitting fuel to flow through the vacuum line that connects the petcock to the #2 carb. This can be easily checked by removing the vacuum line from the #2 carb and checking to see if any fuel is coming from the line. There should not be any fuel flowing through that line at any time.
If the petcock has no problems, or if after correcting any problems the petcock has, consider the following -
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. It's possible that the floats are not operating freely when the bike is on the side stand in which case you can clean everything well and make sure the floats do not stick when the bike is on an angle. This would also be a good time to make sure the float valve needle and seat are squeaky clean since a little dirt can cause them to leak. This 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
1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)
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