You've lost me there- why do I need to replace the pot? Ant idea about that brass rod?

Carby/Idling problem. Got a Mikuni carb on a F5A motor that wont idle. It seems ok once we get it going but dies once revs go under 1000-1500 rpm.  Also needs petrol poured in carb throat to get it going. I guess its the idling jet/passageway- I've cleaned it out but must still be some crap in there...