Here's a long shot: my 751 (Peugeot engine) started to run rough about 50 hrs after a timing belt change. An old time diesel mech listened to it and said "well, that thing is just slobbering all over itself." Musta been a technical term..... Anyhow, that engine has a flanged injection pump that bolts to the engine housing. He scribed a line in the flange and housing for reference, then slightly loosened the three bolts holding the pump to the engine. With the engine running, he then rotated the pump with a huge pair of slipjoint pliers to achieve smooth running. Tightened bolts down and we're done. He only rotated it a few degrees at most. Obviously, this technique depends on having a similar injection pump and mounting arrangement. Best I can offer.

--- Bobbie-G