Eyeball for the right size drill bit in your drill index that will just barely fit inside, and run it in by hand while giving a little clock-wise twist with your fingers. This should break anything hard loose, and if spiders or mud daubers did their work, it should snag at least part of that material on the bit. A bit of grease spatter/drippings could cause problems as well, but if cold enough to solidify the grease, it should open up easily with a drill bit, and some will be stuck on the bit when you draw it back out.
Bring out the bit slowly while twisting in the closk-wise rotation as if you were drilling a hole...helps keep material bound to the bit fluting and not dropping inside the assembly.
Take a look inside with a flashlight and see how it looks. Blow-gun as Piney mentioned (watch the eyeballs, though), or a drinking staw to your lips can help direct your breath where you want it, and can increase the velocity of your breath.
Hmm...need to look at my gassers soon, too...getting temp swings that can't be explained by anything else other than gas flow issues.
Eric