Dirt will be the cause of the problem, but I should have explained in a bit more detail that the needle and seat (float valve) is in the top cover of the carby and is operated by the float. That is when the float rises it closes of the valve which stops the fuel coming through and when the fuel level drops the valve opens again and the fuel flows (just like a float valve in a toilet cistern). I'll bet your float valve is full of dirt which prevents it from closing, and that's why your carby floods - the fuel just keeps coming.
You'll need to pull the carby top off again. Remove the float and you'll be able to get at the needle and seat to clean all the dirt out. That should fix it and a new filter will help keep it clean.
@D I come here to discuss Datsuns and Datsun-related topics. I'm OK with rational disussions here about non-Datsun-related topics, but you're not contributing to a rational discussion. Someone else started the topic and you chimed straight in, but you don't seem to be able to able to contribute anything that's constructive to the discussion. To be honest it reminds me of years ago when Phunkdoktapok was around (with loads of petty animosity mixed in with the irrational comments), and I don't want to have to put up with it all over again.