A lot of the problem with the heavy throttle, especially on a Foden, was that the linkages were never set right from new. If you made sure that all the levers between the pedal and pump were set at 90 degrees to each other then it made quite a difference, though of course those trucks fitted with either a cable or a hydraulic throttle couldnt be altered really. Overtightening the advance/■■■■■■ friction disc also made them stiffer as well.
Pete.