89 ZXR250 Fuel Flow Problem

[Kawasakidude]

Hey guys I have a fuel flow problem with my bike at the moment which is completely stumping me. The symptom is I will fill it to the top with fuel and it will ride and run really smoothly and how it should untill around 135kms then it runs out of gas. Or at least it acts like it. the tank is still three quarters full at this point. The other wierd thing is it will, after sitting for a minute start fine and take me another ten kms and run out again. I have removed the carbs and cleaned them out, I have replaced all vacuum and fuel lines, I have removed the fuel tap and checked the flow from it while it was installed during this condition, I have replaced the float bowl gaskets, checked the float height (it did not need adjusting), replaced the intake rubber gaskets, cleaned the air filter and box and replaced the inline fuel filter (this was done before this problem presented itself). The bike does not run funny at all in fact its smooth and powerfull and starts first pop every time with minimal choke. I'm feeling a bit silly as I'm a mechanic by trade :facepalm: any ideas? :brick:

[ducatilover]

Clean the fuel tank vent bro, pull he tank cap apart and make sure it's all happy
Or bring it over to the workshop and I'll do it :niceone:

[buggerit]

If you checked fuel flow at the tap when the bike stopped and it was fine your tank breather is fine,I would be suspicious of that
new fuel filter, maybe it has a restriction like a bit of plastic from manufacturing that the fuel can force its way past when the tank is
full but as the tank looses head the fuel cant keep up with demand?

[buggerit]

Checked the vacum diaphram in the tap is ok?

[Kawasakidude]

It had a blocked vent but I will check the diaphragm as well as I hadn't had it apart and I want to make sure this problem doesn't present itself again. Cheers guys!