[abisel]

Looks like 2 screws at the top and 2 screws at the bottom, and however it is attached to the gas valve would free the entire assembly from the unit. Then you can take it to the bench and maybe a shot of compressed air from the air compressor will blow out whatever is blocking the nozzle. And can you verify the orifice is correct for natural gas?

There may be a couple youtube videos on cleaning out the gas distribution lines/nozzles.