Fuel leaking up out of filler cap in gpx250

On my Gpx 250 fuel comes up and out the filler cap when the bike gets
hot. I had the tank off and the overflow pipe is not blocked. The
leak happens even when the tank is not full. I know that the seal is
probably not too good (since turning the tank upside down causes the
leak also (should this happen??), I don't understand how the fuel gets
up to the top of the tank however (when it is not full and right side
up on the bike).

I don't know if it's related but I had a few days ago a sump full of
oil and petrol ... Changed the oil last night and it seems ok now.
The fuel petcock seems to be turning of (there is a bit of a dribble
after it does turn of) - checked by sucking on a straw on the vacuum
inlet.

A little confused what to check - probably need a new gasket on the
fuel cap but I don't think this is the complete problem since fuel
leaks out the key hole...?

Any ideas would be appreciated.

Thanks

Peter Cupit

 

Are you sure you're not running the bike with the fuel tap in the PRIME
position?

 

There is no prime position on this bike, I had to put a vacuum on the
petcock ( with a straw ) to get the thing to start - there is only
reserve, on and off. Fuel flow is meant to only occur when engine
turning.

 

What year is the GPX?

 

97

 

How did you check this? Can you blow through it while it's connected
to the tank?

It certainly sounds odd.

The vacuum petcocks do tend to fail eventually, on mine it was at the
15-year-old mark. It failed in that the vacuum function no longer did
anything, so the tap became a "standard" one. If yours didn't turn off
properly (ie. the dribble) and one or both of your carburettor float
valves is a bit dodgy then that's probably how you got a sump full of
petrol.

Well, it sounds like your fuel tank is somehow getting pressurised.
The leakage might be fuel vapour condensing on the upper (inside)
surfaces of the tank and getting forced out by the pressure, but that's
just a wild-arsed guess on my part.


BTH

 

I checked the overflow connector with a car tyre pump - air got through
ok... (Now that I think of it anything else in the pipe would have got
through also..) The pipe itself I checked the same way - it does need
to be replaced as it has a rip in it.

I don't think the overflow is working even through it isn't blocked.

I talked to a guy at a bike shop here in Nowra and he is suggesting
that the internals of the fuel cap are faulty - had no idea it had
anything complex in it..

Peter Cupit

 

[confused face]
There's two types of bike taps.
"Normal" on-reserve-off or
"Vacuum" on-reserve-prime (and no fuel flows when the engine isn't running
unless it's in "prime").

 

They've got a few parts to them, as you'll find out if you start
disassembling one. ;-)

Have you got the service manual I made up? Do a Google for
"GPX250Manual.pdf" and you should turn up a copy.


BTH

 

I nearly suggested a stuck fuel cap, but I thought... nah with all the
complicated stuff you are talking about you'd already have checked that

Do you get a pressure 'woosh' often when you open your tank?


G-S

 

ssshhhh
(if he can't work out that for himself bikes may not be a good idea)

 

Datz zacchery wot I woz finkin'.

 

You'd think that would be the sensible thing, wouldn't you?
Unfortunately Kawasaki decided that for the GPX250 what you really want
in a vacuum fuel tap is Off-Reserve-On.

Even when you set it to "reserve" you still need to have engine vacuum
before fuel will flow, so if you've cleaned the carbies you need to
either use a bit of suction hose to prime the carbies or hope that your
battery will crank the bike over for long enough to fill them.


BTH

 

I think my tank vent isn't working...

 

btw thanks to all who posted

 

or roll start :-( very undignified.

 

Well bugger me!

My apologies Peter.

 

There is sometimes a slight pressure release. Before last week I had
not thought about the whole pressure release system should work. Now
that I have taken the cap apart and seen the little gaskets, small
holes and channels and etc in there it's pretty clear that the most
likely failure isn't the overflow pipe getting blocked. Still
hard to know which bit of the cap is faulty - suspect either the rubber
seal on the key barrell or the big paper? gasket just under the cap
(there are little channels just here where the fuel flows in and then
out when the pressure is high enough) The little rubber pressure
'sensors' seem ok so I think the pressure just gets high enough to
breach the top gasket before the rubbers things let it out around to
the overflow.

btw none of the holes or channels in the cap were blocked...

New assembly costs $119, might try to make a new paper gasket for the
top...

PC

 

So, are you in your prime? Then there's the tap on the Moto Guzzi Sabre.
Vacuum tap, no prime.

Theo

 

"Knobdoodle" wrote

There's more than two types of bike taps Clem. Mine has on and off, no
reserve. The Sabre Helen had had two screw type taps which could only
be accessed by removing the sidecovers (they were only there so you
could remove the tank) and a vacuum operated flow gadget in a place
impossible to access. The scooter has no tap and a vacuum flow control
valve also.

Theo