Yellow flames usually mean either sodium salts or hot soot particles. The shooting bit makes me pretty sure it’s clogged with one of those two, although it could be a sudden burnoff situation more than actual pressurised shooting, without seeing it myself.

Others have suggested possible root causes; I have less experience with this particular thing than combustion in general. Taking it apart, if possible, should give more information. If not, you have to figure out how to wash it inside, or change combustion conditions to increase air relative to fuel and burn off any built up soot.