Oh I´m sorry...
but, maybe - my post could although be interesting for you, most of the Petromax users have dumped the steel burner, because of the several problems, me too!
For better kerosene-gas/air-mixing try to process the air-inlet of the mixing tube with a countersink, this will lead to less turbulences and better airflow.
The needle should be visible at a length of about 1mm (not more), when the valve ist closed.
When tank is pressurized and no inner mantle ist mounted, the kerosene should shoot out straight upwards in a thin jet when you open the valve without preheating the carburettor.
Best regards
Jürgen