Thanks for the response.
I inspected the throttle handle assemby before posting my original request. The assembly is intact, but the cable doesn't spring-back automatically. I'm not seeing any kind of spring in the throttle handle; perhaps the spring in the needle-barrel assembly is intended to actuate the handle back to low "on its own".
I'm going to "goose" the carb needle assmbly by hand (while running) when it gets light tomorrow. I know that this probably will not work. I'm not doing it in the dark, or else my neigbors would wonder if I lost my faculties.
Obviously, I'm no expert, but I'm having a hunch that I'm running too lean, and need to get more gas into combustion. I was getting better than 150 miles/gallon before the issue arose.
But who knows, perhaps I'm completely not seeing something, like not knowing what a loose clutch plate feels like.
I'd appreciate any responses.