I have a 850 Diesel 172 cu that lobes real bad at low rpm's. Had pump and injectors rebuilt at a cost of $1400 and tractor has sat for 7 years with occasional starting only has about an hour on motor. A good friend with over 40 years tractor mechanic experience rebuilt the motor not sparing an expense it was the last thing he finished before cancer got him that's why it has sat. Now wanting to finish it but can't get it to run without lobbing and blowing white smoke. Pump shop says it went bad from sitting NOT buying that. Checked compression timing and valves all cylinders where 295 on compression which is low but can't spin it @ 1000 rpm's with the starter. There was a guy I think named Denny on here that had the same problem but never came back to tell what he found.