How old is the gas? Did you clean or drain the tank?
If you trace the fuel line from the inlet at the carb all the way back to the gas tank outlet, and you don't see a canister of some kind in the way, the fuel filter was removed for who knows what reason. Honestly, it looks to me like something was in a hole in that bracket above your brake booster, but that's just an observation. Subaru's are luckily cheap for most parts. Don't try to clean plugs when it costs you less than $10 to buy a full set. If you have an old car with a carb, you really should pick up a tach/dwell meter and a vacuum gauge.