problem on the bx's, if they're slowing down, sometimes the linkage is coming loose or off. If left loose long enough the link wears out, as does the trunion arm. If it FALLS off, it's kind of a pain in the backside to put a new one on it. But if it's just loose, you can often just tighten it back up and be good to go for another decade or three.
Follow the linkage from the pedal to the transmission and inspect.
Follow the linkage from the pedal to the transmission and inspect.