Do both engines pull fuel from the same tank and filter? This is a long shot, but try swapping the fuel hoses at the point where they connect to the engines if there is enough slack. That will at least eliminate failed bulb or clogged hose.

Did the engine that still fires take longer than normal to fire up, or did it start and run normally? If it was slow to fire or runs rough, it sure sounds like a fuel problem. You may have gunked up the carbs on the non-starter enough so that it is too sad to start.

If the running engine started up no problem, I would look next at the electricals on the non-starter.