Engine fire

Adjusting my carbs, playing with the needle to allow more fuel, and I give it a test start. It backfired hard through the carbs and ignited the airbox. Good thing I had a fire extinguisher handy! There doesn't appear to be any visible damage, but after a thorough cleaning (that stuff gets everywhere), it won't start.

Should I simply readjust my needles? If so, where should they be? I don't want this to turn catastrophic.

Where should I start inspecting for internal damage, if there is any?

Got it started, sounds normal other than regular backfiring through the exhaust. I believe one cylinder isn't firing and is igniting in the headers.