can't stop carb overflow

[bunnysZ]

not a zed but a KLR
carb keeps overflowing through overflow pipe underneath,
butterfly has been adjusted and adjusted jet cleaned carb cleaned , no splits in drain pipe inside float bowl , when tested on a bench with a petrol tank it does not leak, but as soon as i put it on the bike and fit the tank , turn on the petrol it overflows again..?
any ideas.

[z1bman]

have you thoroughly cleaned out the tank + fuel tap

[bunnysZ]

no would that make the carb leak , as it did have a fuel filter on it before which i threw away.

[PAULJAC47]

Hi Bunny,when you test on the bench with a tank is it the same height above the carbs as when on the bike? just a thought it may be the head heigh.t if it more when on the bike may be just enough to overcome the float valve.make a manometer and strap it alongside the carb body,this will show you the fuel height,have you tested the float for leaks? Good luck Paul J

[z1bman]

even though you have a fuel filter minute particles will still get through + cause the fuel valve to not seat correctly . remove the fuel tap + empty the fuel into a clean container to see if there is any rust particles

[Pigford]

Have you checked the BRASS TUBE in the float bowl - they can split

[zmaxmotorsports]

Does it do it all the time,is it a mechanical or vacuam petcock?

[bunnysZ]

brass tube inside is ok and its a mechanical type

[gray]

I had a problem on my GPZ9 last year , checked all the usual things , zilch.
then I had a good close look and saw it was leaking from one of the T pieces that accepts fuel from the hose and feeds it to 2 adjacent carbs. There's O rings in there that can perish , and leak if there's enough head of pressure and it looks like it's coming from the carbs but they'e fine when you drop the float bowls and check everything inside.
Trouble is you have to split the carbs to get at them , and the things are relatively dear , and you might as well do both T pieces since you've stripped it that far so that's 8 you need on a GPZ. They look Ok at first , then you roll them between your fingers and you see all the little cracks round the periphery.