If it has been a little while since the last usage, it is likey a paper nest inside the burner, I had the same thing happen on mine a time back. Paper wasp nest gets inside and once you start it up, it burns smokey. Look in with the flashlight, will probably see remains. If it is a nest like this, the smoke will stop soon as it incinerates, if it is the air mixture it will continue. If air mixture you may notice the sleeve is loose, because it wasn't doing that before, right? If tight, not lileky it is the mix.