Z900 A4 fuel leak any ideas please?

[Gray17]

Good evening Guys.
Not having much luck at all with the rebuild and the fettling seems to be numerous.
Ok so if you read my previous post you will know I've just completed a full rebuild of my Z900 A4 as it was previous import and done to prev owners whims, i not only set about re building it but also putting back to standard, i have re used original parts and refurbed where possible or pattern where not.
Anyway bike refused to start, thanks for all the advice on that, now got bike running but found overcharging 15.7v, so ordered new combined voltage reg, which finally arrived and duly fitted,in the meantime I've been wrestling with a carb leak from L/H carb overflow pipe. Even when tank tap turned off, so stripped tap and checked all seals, which looked ok rubber very supple, re fitted everything and sat tank on blocks to simulate angle on bike with drip tray under twin outlets , with tap turned off, approx 1 gallon of E10 in tank, left overnight, fuel in tray next morning, so assumed tap faulty, ordered new tap 2hich again arrived and fitted, no leaks, but same result fuel pours out of overflow on L/H carb. Now bike is upright on main stand not on lazy stand, all carbs have same float height, i have removed float bowl and if i physically lift up float it stems fuel flow showing valve working ok, obv i cant see float when bowl in place, but everything feels fine and moves smoothly. The tabs on all 4 are bent the same, the other 3 are fine and dont overflow.
What i cant understand is even if i turn tap off fuel keeps pouring out of L/H carb overflow far more then in the pipe, how is this possible?
Its a new tank def no corrosion or sediment, brand new tap, new rubber hose and carbs all cleaned and checked, floats set statically on the bench, all close manually, other 3 carbs work fine. Could it be a faulty float? But why does fuel keep coming out even with tap off.
I have removed tank to re check tap using tray under outlets.
This bike is starting to do my ed in ( Yorkshire term!)
All i want to do is ride it after all my work but it doesnt want to play ball.
Suggestions welcomed.
Thanks

[warren3200gt]

Sounds like the float is sticking on the bowl side. When bowl off works fine, when bowl on overflows. Can only be a clearance issue between bowl and float.

[warren3200gt]

Another thought. With the bowl off fill it with fuel and see if level drops. If it does then the overflow tube has a crack.
Which means when the level drops from dumping fuel from the crack, it refills and then repeats again etc etc.

[Gray17]

Thanks Warren, i will check the overflow pipe as got float chamber off at moment, i assume you would have to replace the float chamber itself if overflow cracked.
As for sticking again thats possible, but impossible to verify as once float chamber back in place you cannot see if its catching. What i could do is swop the R/H carb float over with L/H one see if fault moves over which will prove float assum8ng their identical?
Cheers

[warren3200gt]

If the overflow tube is cracked split it can be replaced but it's easier to sleeve it on the outside with some bass tube then solder it in place. If you've got an radio control model shop near you they are a treasure trove for little odds and sods like brass tube, piano wire to make springs, small tins of enamel coloured paints for switches etc.
Swopping the float bowls won't work. You'd need to swop the floats as it's these that are going to be bent and catching.

[zed9]

Could the float bowl have a leak and not floating correctly or be heavier than others for some reason or poor seal on float bowl valve to body, damage on valve rubber end?

[Ultim8pc]

Cracked overflow tube
Float catching on Gasket or body

[Kev1R]

The cracked overflow pipe sounds bizarre but I experienced this issue some years ago on my Z1R. Not sure what causes it - maybe vibration / stress. In the end I acquired a new float bowl through Dave Marsden. (Although I also bought most of the carburettor that went with it.)
If it is a cracked pipe I reasoned that you would have to be careful that any adhesive for repair would not be soluble in petrol as I didn't want any of that going into the intricate carburettor workings. Hence I went for the 'complete replacement' option. That was back around 1990 and there may be better alternative options now.

[Grog]

Hi Gray;

As per most of the replies abouve, most probably the float catching somewhere - I had it on the No.2 on mine after a carb refresh. Turned out that the float was JUST fouling somewhere on the float bowl (my money was on the new gasket being just bigger than the old, though not noticeable to the naked eye) - like you I was at the point of tearing what hair I have left out. I ran an emery board round the inside gasket faces, and the problem went away. Warren's plan for checking leaks in the bowl/overflow should confirm or discount that as the problem.

The other thing that's puzzling though - you say the fuel keeps coming even with the tank tap off - so where is it coming from? Although there always seems to be more than expected in the line from tank to carb. Easy way to get a rough idea is to pop off a fuel line from both ends, fill with fuel and then measure that. Anymore than that and it must either be coming through the tap or from the adjacent carb - though if you're on the main stand and all the rest are working as advertised I've no idea how!

TTFN Grog

[Ultim8pc]

Fuel taps passing fuel when off is common. OEM taps degrade and even the new repro ones are junk and pass.

[Gray17]

Thanks for replies guys and suggestions, i've been out in garage, firstly noticed float is slightly bent so straightened that, also valve tab bent quite a bit compared to others so straightened that too.
Next created a test for leaking overflow, glass with bowl on top the bowl filled with water and float on top, float does float which is good and no leaks so far into glass see photo not ideal but it works to test.
I read Zpowers suggestions to put a 2nd washer under float valve rather then bending tab so now done. Will leave test till after lunch see if any drips in glass, as fuel was pouring out of overflow got to assume if no drips tube intact with no split. As for float sticking think this may be most likely will check all surfaces as did fit new gasket set. Its also hardest to test as once bowl in place you cannot see if float catches! Have noted that the ones ive fitted not the best so may have to get new set although bowl to carb body not leaking at all. As for fuel flowing have left tank on blocks overnight with drip tray 7nder outlets, bone dry this morning so looks like new tap doesnt leak, perhaps the flow was what was left in pipe but seemed a lot, assumed once level dropped below drain height overflow would stop, but it didnt, maybe should have left it longer?
Will keep you all posted.

[warren3200gt]

Using fuel instead of water will tell you more Graham. If there is a crack in the overflow it'll be full of fuel. Fuel and water don't mix so the fuel would effectively be a barrier to any leaking water.
As the overflow tube sits higher than the bowl surface you could try putting your finger over the outflow end and blowing down the inflow end. You'll feel if theres a leak as your cheeks will deflate

[Grog]

Oooh! Oooh! Liking Warren's idea to blow down the tube to check for leaks - but why stop there? Leave the bowl full of water/fuel as shown. Stick a bit of pipe over the inflow end to give your nose clearance from the fluid. Finger over outflow and blow. Bubbles in liquid? Deflated cheeks? Cracked pipe. I claim (partial) credit for the new-fangled 'fart-in-bath' diagnostic method!

TTFN Grog

[Gray17]

Hi Guys, well yes tried the blow method down tubes already couldnt hear any leaks, the glass was to check if any cracks on overflow pipe, not ideal but it does its job. Best i could come up with on spare of moment and needs must!
Re fitted everything to carb with 2 seating washers on float valve as per zpowers suggestion, it now doesnt overflow, but still got a problem as now got fuel starvation on pot 1 ie L/H carb where leak was , i can now run bike but refues to tick over as L /H carb now not getting enough fuel so not running correctly, other 3 exhausts hot , no.1 only hotish showing not firing correctly.
On the plus side new voltage regulator works perfect at 13.6v at 4k not blowing fuses or bulbs. So thats one prob solved.
Imconvinced it is the float at fault for initial leak and now not getting enough fuel. Still a bit to go. Its so frustrating!

Update: opened carb up on bike again bent tab a fraction, replaced bowl and undid drain screw fuel came out full flow so know chamber now getting fuel, turned tap on and it pours out of overflow again.
So you have 1 way where you dont get enough fuel or bend tab a fraction and it overflows again, this is getting stupid, i must be missing something, i may have to get new fuel valve although it seems to work perfectly, im still thinking somethings catching the float, but nothing seems to be that i can see argh!!!!!!

[warren3200gt]

I suspect that where you straightened the float it is no longer sticking ng/catching on the bowl/gasket. However where you have double washer Ed the needle valve seat you have effectivelly dropped the seat inlet hole lower so the floats now can't drop low enough to oped the fuel inlet fully. Once a little fuel has entered the bowl the floats have risen and closed the needle/inlet meaning the fuel level in the bowl is very low.