Nozzle Cleaning File Tip Set - Superior 

This is no ordinary nozzle tip cleaner set, this superior nozzle tip cleaners set includes 14 needle files with 12 different size orifice files plus 2 twisted wire burnishing probes as well as our own special design of nozzle scraper and tip face file with two different cross cut file faces so as to dress the nozzle face.

To use these correctly is very important so that you do not damage the nozzle.
When cutting, welding or brazing et cetera any "pop" can liberate small particles of oxide which can lodge on the inside of the nozzle orifice.  When this happens on a welding nozzle the welding cone become mishaped and difficult to use plus the nozzle stability can be upset.

Cool the nozzle down in water
Remove the nozzle from the mixer / torch handle so it is easier to work on.
Look at the nozzle tip face and orifice to see if you can see the oxide which is causing the problem.
Having quenched the nozzle it may be possible to pick the oxide off from the nozzle tip.
If not then place the tip cleaner file on a flat surface, with the nozzle tip perpendicular to the file surface dress the nozzle tip face until the oxide is removed, finish with the smoother cut file face.  If there is no oxide / spatter on the nozzle tip face then move on to clean the nozzle orifice.

To clean the nozzle orifice 
First try the twisted wire burnishing needle - these do not cut but can be useful to knock off small balls of spatter / oxide from the orifice walls.  - Test nozzle flame shape

If flame shape is still not correct
Pick a nozzle orifice needle file which the smooth part easily fits in the nozzle orifice.
move the needle file only along the nozzle orifice axis, never move sideways as this will produce a bell mouthed hole and damage the nozzle.
Move the needle file into the nozzle orifice until the serrated file teeth enter the orifice, if there is resistance and the file stops - STOP - take the next smaller size needle file and start again.  Get to the point where the needle file passes in and out of the nozzle orifice then move back to the larger size needle.
Once again test the nozzle flame shape.