1979 KZ1000 st leaking gas

Hey All,

I just purchased a 1979 kz1000 st. Im very excited about this one. According to the seller, the carbs have been rebuilt. I'm noticing that the carbs are leaking gas when I park and turn the bike off for a while. It is coming out the drains below each carb. I know it should do this when the petcock is set at the 'pri' position, but it does this at the 'on' position as well, when sitting. First question, should there be something covering these drains, i.e. overflow line? How do I remedy this situation, as it appears that the leaking stops after a few minutes when the engine is running...but only after all the extra gas is burned off? It appears to be dangerous fire hazard.

Yes, there should be overflow lines which would just put the gas on the ground instead of under the carbs. There are a few possibilities, your vacuum operated petcock could be leaking meaning that gas does not stop flowing when the vacuum caused by the running engine stops.

More likely, however, is that a)your needle&seats are worn and not sealing to stop gas or b)your float levels are set incorrectly.

Most likely it is the float level if the carbs have been rebuilt. Because your floats are not rising at the correct time/height, gas is continuing to flow into the carb and then through your overflow. This would also explain why it only happens for a few minutes after the bike is shut off. The excess fuel in the lines is draining out, it isn't constantly leaking out of the tank.

There are cheap little tools that you can screw into your floatbowls to help set your levels but it is a fiddly and PITA job.

Thanks much...should the overflow lines be seperate lines or 1 line with 4 inputs to connect to each carb? Also, when you say cheap little tools to screw in the float bowls, do the carbs/bowls have to be removed for this?

bowl drains should have tubing going aft of the engine cases.
I would rather see it drip on the cases instead of gassing up my rear tire. :blush: Is your tank rusty? Fuel is leaking from 4 bowl vents, all the carb cleaning in the world doesn't stop a rusty fuel tank from messing with a vacuum petcock. I see this all the time. Maybe a bad petcock diaphragm. it's leaking from all 4 , bad fuel needles or crud, high float level.
:whistle: no filter made will stop the red rusty crud from fouling a new carb clean job. petcock diaphragm may be held open by crud/rust? :huh:

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bonzeyt wrote: Thanks much...should the overflow lines be seperate lines or 1 line with 4 inputs to connect to each carb? Also, when you say cheap little tools to screw in the float bowls, do the carbs/bowls have to be removed for this?

The overflow lines are just separate small fuel lines that run out behind the motor to the ground. Any bike shop should have lines that would fit and you just cut them to length.

To check the float level, the carbs do not have to be removed. The tool is just a screw that fits in where the drain screws on the float bowls are with a tube attached to the end. To check the level, screw the tool in, have the bike sitting level (on centre stand) and hold the tube up to the side of the bowl you are working with. Turn on the gas and the gas will rise in the tube to the level that the fuel in the bowl sits at. Your manual will tell you how high it should be. To adjust the levels, the bowls do have to be removed. The level is then adjusted by bending the small tang/blade on the float to change how soon it contacts the needle. Then remount the bowl, recheck, etc. It is just an annoying task and can be difficult to get at the screws for the bowls.

This is the only tool I could find off-hand like this. It is so expensive because it is a Kawasaki part but there are aftermarket versions too that run $5-10.

turboking wrote: Fuel is leaking from 4 bowl vents, all the carb cleaning in the world doesn't stop a rusty fuel tank from messing with a vacuum petcock. I see this all the time. Maybe a bad petcock diaphragm. it's leaking from all 4 , bad fuel needles or crud, high float level.
:whistle: no filter made will stop the red rusty crud from fouling a new carb clean job. petcock diaphragm may be held open by crud/rust? :huh:

Not vents, overflows. Also, if the vacuum petcock was the problem, gas should flow constantly instead of stopping after a few minutes as described. Either way, rebuild kits are available for the petcock and it is an easy job.

okay, the tube in the bottom of the bowl . i call it a vent /overflow :evil:

bonzeyt wrote: Hey All,

I just purchased a 1979 kz1000 st. ....I know it should do this when the petcock is set at the 'pri' position.....

First - NO it should not do this regardless of the petcock position. Floats inside the carbs are suppose to control the fuel level and never let the level get so high as to over flow.

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 reoccurrence 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 of alcohol and see if it leaks. 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

turboking wrote: okay, the tube in the bottom of the bowl . i call it a vent /overflow :evil:

Just wanted to clarify as there are actual vent tubes on these carbs in addition to the overflow drain tubes.

If the floats are set correctly, and the needles/seats are good, the carbs will not dump gas out the overflow tubes. The tapered tips of the eedles should be polished dead smooth (hand drill and #600 paper works). I also polish the inside of the brass piece they mate with. That interface has to be perfectly smooth or it won't seal.

It's typical for the carbs to leak if the petcock is left in the PRI position. My bike is in pretty good shape, including the carbs, & it will leak in PRI. If the petcock diaphragm is bad, it will leak.

Check the petcock. Disconnect the fuel line & see if it's leaking (ON or RES & engine off). If necessary, install long tubing & direct it into a container. In the mean time, install tubing & route it into a clear juice container to collect the fuel & cut down on the fumes.

did you spill some gas and it is going around the outside of the carb?