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XT600 3AJ leaking fuel from carb drain XT600 3AJ leaking fuel from carb drain
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  #1  
Old 22 Apr 2020
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Question XT600 3AJ leaking fuel from carb drain
Hi,

Finally found why my XT600 is smelling so bad.
Maybe 1 drop of fuel per couple of min is draining from the carb drain. Can't see whether it's from the actual drain hole or the drain hole plug.

Either way I removed the plug but don't see how any dirt/wear could be the cause of this. It all looks very simple and last year I already completely stripped and cleaned the carbs.

I did noticed the plug has a grove for what looks like an o-ring, however I can't find it on any diagram. Mine has nothing there.



Any idea?

Thanks

edit: found this:

Quote:
I don't know about the XT600Z, but my '94 XT600E did not have an "O" ring on the bowl drain screw. It is a tapered fit and is supposed to block off the drain passage as is (the drain screw has a tapered end to fit a mating hole; the drain screw area cuts across the drain passage at an angle so an "O" ring outside the drain passage does not help). If the drain screw THREADS are leaking, then you might be able to get away with some non-hardening, fuel-proof liquid gasket material. I replaced mine because it was leaking out the bottom and the screw head was boogered from many drain cycles. I guess you could always insert a tiny neoprene bung in the drain hole as a temporary measure.
Should've searched first.. Is this true? Is the tapered bit responsible for the blocking? It looks pretty smooth to me.
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  #2  
Old 23 Apr 2020
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very odd that fuel would get past the screw, the taper cone is what seals and it shouldnt leak really
most likely fuel tap not really closing and fuel then getting past the float valve.
many times it's just the o-ring of the valve seat that needs changing
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  #3  
Old 23 Apr 2020
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Quote:
Originally Posted by turboguzzi View Post
very odd that fuel would get past the screw, the taper cone is what seals and it shouldnt leak really
most likely fuel tap not really closing and fuel then getting past the float valve.
many times it's just the o-ring of the valve seat that needs changing
It's leaking from the screw threads. Not sure if it's also leaking from the drain hole itself, or whether it's is simply dripping to it from the threads.

My fuel tap is always on, the carb float should stop it, right? That's what it's there for. Even so, there is always fuel in the bowl, regardless of fuel tap or float valve? So the tap should seal regardless.
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Old 23 Apr 2020
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The float is designed to hold back some of a flow with a running engine, not the entire contents of the tank for days at a time. That's why they fitted the tap. With the tap off a bit of fuel in the bowl can leak out or evaporate not the whole tank and then the float can stop trying. It's good practice to turn the tap off a few hundred yards from the last stop of the day. If this is your trouble, hope you caught it in time. Honda twins initially leak along the intake and contaminate the oil via the cylinder head. Could be worth checking the oil for increased level or smelling of petrol.

Andy
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  #5  
Old 23 Apr 2020
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Polish the tapered end of the screw with some metal polish and put it back. If there's any slight nicks or marks the polishing should help remove them. If it's still leaking, take it out again and bang a cork or similar into the hole to seal it. Don't ride it like that but leave the fuel turned on for a bit. If you're still getting a leak it's the overflow and you'll have to have a look at the float valve. It doesn't need much to stop the float valve from sealing.
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Old 23 Apr 2020
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Quote:
Originally Posted by Threewheelbonnie View Post
The float is designed to hold back some of a flow with a running engine, not the entire contents of the tank for days at a time. That's why they fitted the tap. With the tap off a bit of fuel in the bowl can leak out or evaporate not the whole tank and then the float can stop trying. It's good practice to turn the tap off a few hundred yards from the last stop of the day. If this is your trouble, hope you caught it in time. Honda twins initially leak along the intake and contaminate the oil via the cylinder head. Could be worth checking the oil for increased level or smelling of petrol.

Andy
Hm.. are people seriously turning off the taps after every ride? That's pretty annoying. I guess I could use just the one until I need reserve. Don't think there's fuel in my oil. Just replaced it and would've noticed the tank getting fuller. I had to add a bit after my first full ride, which was after 1 full week with the petcock open.

Quote:
Originally Posted by backofbeyond View Post
Polish the tapered end of the screw with some metal polish and put it back. If there's any slight nicks or marks the polishing should help remove them. If it's still leaking, take it out again and bang a cork or similar into the hole to seal it. Don't ride it like that but leave the fuel turned on for a bit. If you're still getting a leak it's the overflow and you'll have to have a look at the float valve. It doesn't need much to stop the float valve from sealing.
It looks pretty clean. Already polished it but not with some metal polish. Will try that and otherwise guess I'll get the carbs off. Thanks
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Old 23 Apr 2020
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Btw shouldn't the carb overflow from the overflow tube before flooding the engine?
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Old 24 Apr 2020
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Quote:
Originally Posted by Doubleyoupee View Post
Hm.. are people seriously turning off the taps after every ride? That's pretty annoying.
I do since there is no vacuum on these bikes. I find it's more annoying to find the tank drained after being parked all day.
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  #9  
Old 24 Apr 2020
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fuel seem to come from the threads because its leaking at the cone of the screw



otherwise, nice dilemmas.... in my british bike days, with crappy cork tap seals and even crappier amals floats/needles, yes, you would close the tap after every ride.... back then old iron was all i could afford, got used to that quickly


with japanese bikes, it depends... if there was no problem with regular taps, we wouldnt have vacuum taps, right? so they exist for a reason, even good float mikuni/keihin needles have a hard time ensuring no fuel goes past.


in my DR350 i can leave the tap open for a week, doesnt even leak.
in my XT600 it will start leaking fuel in half a day.
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Old 24 Apr 2020
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Quote:
Originally Posted by Doubleyoupee View Post
...
Hm.. are people seriously turning off the taps after every ride?
...
after some recommendations from this forum, turning off the tap (and also allowing engine to run for a while) became steady custom for me - not after each ride, just for overnight, despite of the float never leaked.
to be honest, on the other hand, when sometimes a ride unexpectedly becomes that day's last ride and later, when a warning message jumps in the mind that tap is left open, that is more annoying
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Old 5 May 2020
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Today I did the "tube test", put a transparent tube on the side of the carb and connected that to the drain.
With tank 50%, when I open the drain tap, the fuel stops at around float level as expected.

However, with a full tank, the fuel rises way above. Looks to me the float can't stop the fuel with a full tank.

I wonder what happens during e.g. idle? The fuel level was rising pretty quickly, I wonder if it doesn't rise too much during riding and overflow... It runs fine all the way through a ride though.

Kinda doubting to buy a carb revision set..
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Old 6 May 2020
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look at part #10 here, its the valve seat. as you see it has also an o-ring that doesnt have number. very often it dries and lets fuel go around.



check it out before you buy a kit, might be a 5 cent fix.
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Old 6 May 2020
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Quote:
Originally Posted by turboguzzi View Post
look at part #10 here, its the valve seat. as you see it has also an o-ring that doesnt have number. very often it dries and lets fuel go around.



check it out before you buy a kit, might be a 5 cent fix.
Thanks, already bought a kit. I'd rather replace the needle while I'm there.
Also going to check the overflow situation and how/why it comes out of the bottom.
Also got a petcock repair kit x2 while I'm at it. The right side one is leaking just the slightest even in OFF position, even though I already had it open to clean once.

Oh well, hobby money!
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