Started my 1957 series 2 2.0 diesel today. OK at tickover initially but would not rev, almost as if the linkage was broken (it's not - I moved it at the pump end). As I scratched my head the revs started to build up but still independent of the throttle. Got to about 1500rpm I suppose and I stopped it for fear of damage. Now it won't start at all. Any clues please before I start taking things apart unnecessarily?