Carburetor leaking [Archive] - Kawasaki Motorcycle Forums

Carburetor leaking

05-17-2019, 04:12 AM
Hi all,

New to this forum. I have an old Kawa GPZ 900 R (1988 ) and have some trouble with the left carburetor leaking petrol. Petrol is pouring out from the air inlet as well as from the inlet into the cilinders when the motor is off and the throttle is not used. I am not a Kawa pro, but i have a hunch the left carb is stuck somewhere on the inside.
I have tried giving the carb some small taps to see if that unlocks the stuck part inside but no luck. Possibly someone on this forum can tell me what the problem is and how to solve it? Im mailing from the Netherlands, my english isnt perfect but should be ok.
Thank you all for reading and possibly helping me. (ps i have no experience on forums so hope i am posting on right manner)

regards Smuzzi

05-17-2019, 07:21 AM
Sounds like the float is sticking or the float valve is sticking/leaking.

The carbs will have to come off and the float bowl removed to see the problem.

05-18-2019, 07:23 AM
Thanks David1963

Pfew.. sounds like a lot of work for such a small reapir but if this is the way i guess it has to be done.
I havent removed and opened/cleaned vacuum carbs before, is ther anything special i need to know in the proces?

thanks again

regards Smuzzi

05-18-2019, 08:38 AM
This is rather common in old carburated bikes. ….in general, fuels flows by gravity from the tank to the carburetor's bowls. Usually through a vacuum operated petcock or tap. Petcock is opened by engine vacuum when running. In the carb bowl, there is a float with a rubber pointed valve (needle) which shuts the fuel when proper level is reached.

If a carb is leaking when engine is not running, then both, the petcock and the carb valve are leaking. The petcock is a rubber diaphragm and they sell kits to 'rebuild' them, or it could simply be replaced for a new one. Usually there is a filter on top of it inside the tank.

….the carb, either, the rubber point in the valve is bad, or there is some dirt preventing it from shutting. Doing replacement/cleaning work on motorcycle carburators is very easy and quick once the carbs are out. The hard work is really getting them out, and back in, which is usually a pain and looks like impossible mission when you have never done it before. But is of course doable, once you know how.

Usually you have to mangle the intake rubbers into the air box to get the rack out. It is also tricky to align 4 carbs into these rubbers when installing them back, as these old rubber is usually stiff. Some recommend softening in boiling water to get them soft. When they are new is a lot easier. Disconnecting and connecting back the throttle cables is also tricky, normally having to loosen them at the other end on the bar first.

….could go on and on...needles to say, you would be much better of if you had the factory manual, and try watching a video of the job on a similar bike if you can.

05-18-2019, 08:46 AM
While you are at it, install a filter in the fuel line before the carbs to keep rust particles from causing this problem again. It has to be a free flowing filter to prevent fuel starvation at full throttle.

05-18-2019, 10:01 AM
Youtube is your friend. Shoodaben Engineering has several videos on the concours ZG1000 it is a inline 4 cyl with CV carbs. He is a carb expert on that bike. I also found videos on how to rebuild the CV carbs on my sons Vulcan 750. A hair drier can help to heat the carb boot and make them softer.

+1 on both the petcock and a float needle leaking. Partszilla, Bikebandet, Cheapcycle parts and others have OEM parts lists. Just search for motorcycle parts. If someone has replaced the original vacuum petcock with a manual one make sure that you turn it to off every time.

05-18-2019, 01:25 PM
The carbs are not that complicated. What I do on my ZN is to remove the carbs and leave them attached to each other. then remove the fuel bowls and diaphragms/sliders, remove the jets and emulsion tubes and make sure all the orifces are cleaned out by spraying carb cleaner through them or using a weld tip cleaner to poke throught the holes. Usually, the fuel needles/seats are the only things that need replacing. The hardest part of the job on my bike is disconnecting and reconnecting the throttle cables.

05-22-2019, 09:26 PM
I'm aware that titling a bike by year is done differently in many places in Europe, year of sale versus year of manufacture. It looks like the last year Kawasaki manufactured the ZX900 was 1986 so I'm assuming that is what you have.
Does the left carb leak when it is on the centerstand or just when it is on the side stand when you park it after riding? I agree with almost all of what has been said here. I haven't seen mention of setting the fuel level and that should certainly be checked when you have them off and cleaned up. I think you are better off using as many of the factory parts as you can clean up. The float valves are still available on Partzilla, p/n 16030-1007 as are the float bowl O-ring gaskets p/n 92055-1222. Other than those I'd try to clean and reuse everything else that is already on the bike.
The airbox rubbers are a pain, and if they aren't too far gone removing the air filter and placing a hair dryer into the airbox to warm up the rubbers between the carbs and airbox can help a lot. If they are still very stiff after heating them up, or if they show any signs of cracking, you should replace them too.
I tend to hook up the throttle cables with the carbs slid half way into place but you can still access the throttle pulley. Install the cables and then slide them the rest of the way in and fight...I mean gently work with the rubbers.