Z900 Carb issues

Just joined this forum. I own a 1976 Z900 . Have done since new. I have always maintained the bike myself. I recently changed the float bowl gaskets on the carbs and can not stop fuel leaking out the joints. all 4 of them! I have tried different gaskets. No change. No leaking from the overflows
Have also installed new float valves.
The bike engine is stock with the original Mikuni VM26 carbs. The bike has 100000 miles on it but still ran strongly until I started messing with the carbs. I have set the float level to 26mm as per specs I obtained on these carbs. That is from the gasket mating surface to the top( bottom) of the floats when upside down.
Rode the bike today and it does not run at all. Fuel starvation??
When I took the reading on the float heights before I changed them they were massively different. The height before was 20 mm. These were as originally supplied and have NEVER been fiddled with until I changed everything to try and cure the fuel leak .
So 2 questions.
Why the leaks?
Why the huge discrepancy in the float heights between spec and what I found on my carbs?
I attach a photo of the bike for reference.
Any advice would be most welcome
Thanks

Welcome, I too have a 900 amongst others. Firslty the gaskets nearly always weep initially until they expand with the fuel soaking into them if they are fibre gaskets. This can take a few days to occur. You can get reusable rubber gaskets which if you fit which won't leak.
Regarding the float heights, always check the fuel level in the bowl using the wet method. Float height can vary considerably when the correct way up if measure set inverted.
The spring in the fuel valve weakens over the years resulting in a non closing valve/seat allowing fuel to continually flow into the bowl if the fuel tap is on or allows fuel to seep through when off.

Keystar sold rubber gaskets for the float bowl and are reuseable multiple times and last longer.
Díd take off and on my carb bowls 5 times for jetting and never had any leak.

www.motorradbay.de/z900a4-yfcg-27r_2-gas...75cb74dca70b7bd60b60

The correct method for bowl fuel level is to use the clear tube with carbs upright and level. It takes time and patience but once the float level is set you will not see leaks if your float valves seal properly.

I agree on Keyster gaskets.

You may have multiple problems, but the wet test is best. Also if your pertiock is not shutting off fuel, it will flood out constantly. Gas is one of the hardest fuels to contain with a small pintle valve like the needle/ seat in the carbs. Mine are not rubber on brass, both sealing surfaces on my bike are both brass needles on brass seats. I also polished mine and it still will dump gas and flood if I forget the petcock in the prime position.

This is a wet fuel level test. As recommended by Steve West, make a holder out of old carb holders, if available or mount the carbs level in some manner. Doing it on the bike is almost impossible.


Don't place the tank much higher than the carbs so the fuel does not overpower the needle and seat.


Measuring the float heights with the catrbs inverted will get you into the ball park. The wet check tells you what is going on without a doubt.

Thank you for the advice. I will do as you advise

I have a different approach to most around here regarding carbs. First thing I do when trying to troubleshoot is to bust them down 100% unless I know for a fact that someone trustworthy had done so recently. Soak all the hard parts in carb dip followed by careful inspection of all parts. The float needles and seats, along with all the brass parts, can typically be reused. I polish the seat with a small piece of gray scotchbrite stuffed into the seat and turned around until the metal is nice and shiny. Reassemble and then do the clear tube test. It's quite common for the fuel Tee's and/or the fuel transfer tube O-rings to be hard and brittle. Replacing those is critical which is one of the reason I always break down the carbs fully. Float bowl gaskets rarely leak in my experience. Even old and crusty ones.

After re-reading your opening statement.. You say it ran strong until you messed with the carbs. I would suggest cleaning and polishing the original needles and seats, retrieve the original gaskets and put the original parts back into the carbs, then do the wet test. As Nessism stated, un-ganging is the best way to clean all of the passages, although a PITA.


I have never replaced anything in my carbs except the rubber booties on the choke "plungers" including the bowl gaskets. After the >close< inspection referenced above.


Self inflicted wounds are sometimes the hardest to undo. I know this all too well. :pinch: