breather pipes never fill up with fuel they are there to draft air into the tank when the fuel is being pumped out if its kinked it'll cause a lack of air meaning the pump can still keep pumping but only a very limited amount of fuel would get through, I had a fuel starvation problem with my bike at higher speeds where the suction was strong enough it would run fine but below 8K revs it would stutter allot.

Kennon