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carb overflow problem
- Slade74
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1981 kz650 CSR
The carbs are draining fuel from the overflows while parked on the kickstand, but do not do so while on the centerstand.
The fuel is definitely coming from the overflow tubes, not an external leak (like a gasket).
Has anyone run into this before, or have suggestions on what to check? Any help would be appreciated.
1981 KZ650 CSR
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- 650ed
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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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- bountyhunter
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That sounds like the fuel levels are set too high. You can check with clear tube. You adjust level by bending the tang on the float. While the bowls are off, polish the needle tips and seats to get a good seal and this problem will be gone.Slade74 wrote: I did some searching, and couldn't find a post with my exact problem.
1981 kz650 CSR
The carbs are draining fuel from the overflows while parked on the kickstand, but do not do so while on the centerstand.
The fuel is definitely coming from the overflow tubes, not an external leak (like a gasket).
Has anyone run into this before, or have suggestions on what to check? Any help would be appreciated.
1979 KZ-750 Twin
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- Zephyrrider
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Mick
1994 ZR750 Zephyr C4.
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- Slade74
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Just trying to do some mental diagnosis before I go tearing into anything.
I installed a rebuild kit a few weeks ago, but have suspected that it may not be shutting off fuel when the engine isn't running. I had to pull the tank to modify the coil brackets with the new dynatec coils. The tank drained through the petcock, despite having no vacuum applied. I disassembled the petcock, but couldn't find anything wrong with it. It seemed to work ok afterward.
1981 KZ650 CSR
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- Slade74
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1981 KZ650 CSR
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- 650ed
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Regarding polishing the seats - a little GENTLE metal polish on a Q-tip should to it; in fact, carb cleaner should normally be sufficient. Do not use anything abrasive or the needle will not be able to seal against the seats. Ed
1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)
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- Slade74
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1981 KZ650 CSR
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- bountyhunter
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I take them out and wrap a bit of masking tape around the threaded portion. Then GENTLY seat into the chuck of my hand drill. Get Q-tip and chrome polish and spin the thing while polishing inside where the needle seats into.Slade74 wrote: Bounty Hunter, the needles are easy enough to polish, but how do you do the seats?
Do similar with the needle except I use a popsicle stick and 600 sandpaper to polish the tapered end of the needle.
1979 KZ-750 Twin
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- Slade74
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Thanks for everyone's help.
1981 KZ650 CSR
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- 78kzturbo
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- Zephyrrider
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Enjoy your riding
Mick
1994 ZR750 Zephyr C4.
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