With my 1992 BB TC2000 Forward Control I dare claim to have one of the few successful "civilian" conversions around. We have put 48,000 miles on her in eight seasons (now total 242,000). She has the Cummins 5.9 and the MT643.
We have always had to use quite stiff accelerator linkage return springs, to ensure proper return when I lift my foot. Recently I had to add a third spring, and now it takes "two men and a boy" to "step on it".
The linkage rod ends are new. The cable feels perfectly free when I move it by hand. (I had the radiator out the other day.) (My BB dealer had the cable rod-end in stock -- very impressive.) So... why is it not returning to idle with only normal spring tension?
Can a worn cable bind up under load, but feel free when inspected? Can something similar happen in the injection pump?
The transmission modulator cable does not seem to be the culprit, as it does not start moving until the accelerator has been moved a bit.
Pedal pivots seem all right. We are theorizing that the cable-wire has worn a groove in the housing and is now wedging itself in that groove. I will buy a new cable assembly. Thanks a million!