Currently I have a foam filter over the carburettor so the breather pipe from the crank isn't connected to the airbox anymore. I notice there is oil coming out of the pipe. 
What could be the cause? A big problem?

Breather pipes breathe crankcase gases which include oil 'mist'. Refit the original filter or put that loose pipe into a catch can of some sort and empty it regularly; before any gets on the road and spoils some motorcyclist's day/life.

dont use catch can.  oil should not be coming out. Use a ram air filter like this one.

 

 

it allows better breathing out from crankcase. you will notice some smoke while engine is warming up, thats the condesation. soons as engine warmed up and running for a while you will notice the smoking is gone.

 

oil should not be coming out.

 

Have you overfilled with engine oil?

Oil is coming out, the OP said so, so I'm not sure it matters what you 'think' should or shouldn't be coming out.

A catch can of some sort will stop it going on the road; that filter will not. Routing it back into the intake properly will save any need for making or buying anything.

 

 

i was more concerned about his engine more so than the road which is wrong i admit. sorry