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Hi, I've an old GPZ900R, carb engine, 4 cylinder. I've done a big-ish restore on it over the years but one infrequent but regular problem ... if the bike is unused for about 2 weeks or more, then when I start the bike, the right hand side outer-most carb will flood. It doesn't happen if I ride regularly, which I typically do. Last summer I did 5k mile Euro trip with no issue.
When this happens, if I drain the float bowl, remove the float valve, refit then it's usually fine. Tapping it with a mallet has proved helpful, or blowing thru the drain valve.
However, today it's continuing to leak altho I suspect the carb bowl gasket is the fault on this occasion.
The carbs were ultrasonically cleaned and full rebuild 10K miles ago. I use premium petrol. The other 3 carbs are perfect, never leaked or had problems. The bike rides great.
So is it likely to be just a dodgy float valve? Or, I'm wondering, the bike only has a side-stand so the RH side carb is higher when sitting, could this have anything to do with it?
Thoughts welcome!
perhaps the float isn't sealing 100% and over time enough fuel can overflow the bowl?
Have you checked the float valve is fully intact and not "sinking" in the bowel when ther eis fuel in there? If you've seen the gaskets perishing, this wont help and maybe suggests the fuel is attacking both elements. Also, when the fuel sits, it can start to form gums over longer periods of time. The whole bike tilting thing could be that the small amount of wear on the float is being exasperated. Have you checked if the new floats and gaskets are newer materials sucks as Viton or PTFE? Also, does it have needle adjustment on the jet or are they fixed port sizes that you can change, as if the jets are too wide it could encourage more fuel to flow through but that would only happen in operation.
just seen that those engines have a vaccum line, the piston could be holding open after operation, so look to see if that is getting stuck.
Thanks all. Visually the existing float looks good, and works 95% of the time, but I guess it only needs a tiny imperfection/wear to malfunction. New float and gasket on order so will compare.
Vacuum line - is this via the fuel tap? If so, it gave me problems ages back so replaced with a simple on/off gravity tap which has been faultless so far.
The jets are fixed size but there's a needle to adjust flow rate, but as you say, would imagine this would be noticeable only in operation, and it idles and pulls very cleanly, all spark plugs similar colour so assuming the jetting is correct.
And fwiw, just gone back to it, started it, no leak at all!!!
Id suspect the float valve needle. Swap it and see.
Hi, new float needle a few days back, all well so far ... thanks for the help
Ok, so had a fab trip around Dolomites and Alps. In 2500 miles the bike was faultless...apart from the final morning...turned on the fuel tap to set off, and carb 3 flooding. Took the float bowl off, wiggled the float and needle, reassembled and all well.
Now back home, I have replaced carb 3 float with a new one, so it now has the new needle and new float. All seemed well, but the bike has been standing for 10days, turned on the fuel tap and it is flooding from carb 4 (which has te previously faultless carb 3 needle and float)
So my conclusion/observations are:
- the float and needle are not the issue.
- typically carb 4 is the flood point.
- the bike is always on its side stand so carb 4 is a high point.
- generally only floods after standing (with a couple of exceptions).
- it can always be fixed by removing the float bowl, wiggling float.
So could air get trapped in carb 4 bowl, and prevent the float closing?
I guess I'm struggling as I've switched float + needle from carb 3 (which had previously never flooded) to carb 4 and it's still flooding, plus it generally does not flood when used regularly. So I'm thinking I can rule out either float or needle and float height (which looks good on checking it).
What about needle valve seat as a culprit?
Any ideas?
If the float isn't leaking and the needle is good I'd check for crap on the valve seat stopping it shutting off properly
Get a center stand. 😁
I've fitted a zzr600 rear wheel which has a wider tyre which rubbed on the centre stand. I did tho once leave it for. Couple of weeks on the work stand and it flooded after that...
Hmm so the flooding is definitely caused by the float and needle valve not closing off the petrol supply.
You've had a new float and needle valve.
Thngs to do next...
1) Check the needle valve seat isn't damaged
2) Check that the float can ALWAYS close the needle valve and that that doesn't change if you tilt the carb' (as it does when the bike is on the side stand)
Always wanted a GPZ900 - I lusted after one as a kid (1980's) and always thought I'd get one eventually but I never did :o(
I would start by swapping the carb that's leaking with one that isn't.
Maybe swap the two outside carbs around?
Then see if the problem follows the carb or stays in the same place.
If it follows the carb I'd then check the valve seat.
Gratuitous pics!
And thanks, think I'll look at switch valve seats next ...