It's had the 030 card since I've owned it, and the Tyga chambers have been on for years. Just threw that in there on the off chance someone might have seen something similar.

I think my next move is to go through the fuel system. Petcock and tank filter are newer parts, and the inside of the tank is clean. Doesn't seem to matter if the tank is on main or reserve. I would have overlooked the breather hole, thanks TuckerBag.