Kz 750 e2 fuel coming out of overflow pipe when engine shuts off

Hi all. I was riding to work today and noticed the acceleration a little rough. It got worse on the way home and I thought it was an ignition issue, felt like not all cylinders firing. I noticed when I shut the machine off to check it the there was fuel around the center stand. I turned the tank valve to prime and sure enough more fuel came out.
I think that one of the carbies floats are too high. Any ideas? It has happened pretty suddenly.

Sorry it is a 1981 with keihin carbies. And thanks in advance for any help

Mirbooya wrote: ...when I shut the machine off to check it the there was fuel around the center stand. I turned the tank valve to prime and sure enough more fuel came out.
I think that one of the carbies floats are too high. Any ideas? It has happened pretty suddenly.

If fuel is escaping from the overflow circuit, it's likely being caused by a dirty float valve, and not from some sudden inexplicable change in float height.

One very remote possibility is that the float happened to spring a leak out of the blue, which is far more unlikely than a speck of crud in the float valve.

If not already done, an aftermarket in-line fuel filter should be installed.

Good Fortune!

Thanks for your help Patton.

I have checked further and the fuel is only leaking from the number 4 carburetor. It is leaking from the drain hose on the float bowl. It is strange, but when you switch the fuel to prime the fuel is just pouring out like the drain screw is loose. I've checked the drain screw and it is tight. Tomorrow I'll check the float height. See picture attached.

O.k just checked float height with clear tube on the number 4 carb only. It's way off. I could see fuel leaking from the carb to engine intake manifold, so I think I should change the oil as well.
For the float needle seat and valve, is it better to get oe or the ones on z1 enterprises ok? Big price difference. But I have heard that only oe is good when it comes to carbs.

Mirbooya wrote: O.k just checked float height with clear tube on the number 4 carb only. It's way off. I could see fuel leaking from the carb to engine intake manifold, so I think I should change the oil as well.
For the float needle seat and valve, is it better to get oe or the ones on z1 enterprises ok? Big price difference. But I have heard that only oe is good when it comes to carbs.

Petcock in PRIME position allows gasoline to flow regardless of whether the engine is or isn't running.

This free flowing gasoline is getting past the leaking float valve and into the float bowl, where it keeps rising until it supposedly escapes via the overflow circuit, at which time the fuel level exceeds spec.

The clear tube test is accurate only when the fuel valve isn't leaking. Because if the fuel valve is leaking, the fuel keeps rising inside the bowl (unchecked by the fuel valve).

When the float valve is leaking, the clear tube test is meaningless, except to indicate that the fuel level is unstable and not being limited by the float valve when the float valve is supposed to closed.

Fuel rising on up past the overflow and into the carb throat indicates that the the overflow circuit is obstructed, or partially obstructed, or that the float valve is leaking so badly that the overflow circuit is overwhelmed by the volume of incoming fuel.

Would suggest cleaning both the float valve and the overflow circuit.

Would also assure that the petcock isn't flowing fuel in either the ON or RES position when the engine isn't running.

Unless the float needle and/or float needle seat is damaged or worn out, a good cleaning of both the needle tip and seat orifice often eliminates the float valve leak and restores the float valve to proper function, without needing any new parts.

Sometimes it helps to chuck a Q-tip in the drill and spin it inside the seat to clean the orifice, using carb cleaner on the Q-tip.

While the carb is overflowing, another trick is to rap smartly against the float bowl with a plastic hammer or screw driver handle, which may also be done with the engine running, which sometimes stops the leak.

Running some SeaFoam additive to the fuel may also help clean the float valve and eliminate the leak.

Good Fortune!

Also clean the fuel tank, look for the source of the crud. Could be rust, or just some crap from poor fuel.
You can drain each carb into a clear container looking for debris, to see whats got into them. You can replace that #4 float valve and reset fuel height there on the bike. But probably best to pull the rack and clean all 4 carbs out, along with the tank.

While the carb is overflowing, another trick is to rap smartly against the float bowl with a plastic hammer or screw driver handle, which may also be done with the engine running, which sometimes stops the leak.

Hi Patton, the above advice did the trick and stopped the leak. Sharp tap from screw driver handle with carb overflowing into plastic bottle. It was good tip. Now I will ensure I fit an inline fuel filter ASAP.

Motorhead, Patton, thanks heaps for your help. I will keep the machine off the road for a few days to find the source of the crud. Very glad the float valve works again though.