I just cleaned out a giant nest of something from the burner tube as our WH would not light.
A time before that, we were getting black and smelly soot, also caused by insects residing in gas tube.
After cleaning, all was good.
On our WH there are a whole bunch of screws, some not real easy to get at. Oh, and those screws are not all the same size, so keep track of which hole each screw came from. And on our WH the little metal burner deflector thing at the end of the tube has three holes. Each hole moves the deflector thing away or closer to the end of the tube, so make sure you no which hole that was attached.
Sometimes I wish I were living in the stone age. Then I would know I'm the smartest person in the world.