85 mack r686 surging

85 r686 is surging at lower rpm between 1000-1200 is the worst. smooths out ok above that but very annoying driving around the yard when almost any throttle will start a surging/bucking show. throttle linkage is tight and return spring on pump is intact. I seem to remember a service bulletin about the ambac pumps with governer/flyweight issues, can the governor assembly be separated from the pump while still on the truck? and any idea what parts need to be replaced? the number off the...

85 mack r686 surging

85 mack r686 surging