WELCOME TO THE WORLD OF 6.3 PAIN....[}:)]
Rich running is caused in Short by a worn Injection pump.Art has had his 600 pump rebuilt for reasonable price in Melbourne,certainly a lot cheaper than the equivalent Toyota Diesel pump.
You can check your cold start mechanism to ensure it's working OK.
Quick checks can be done by feeling the two rubber hoses comming from the top of the injection pump,when the temp guage reads warm,they must be hot,indicating that water is circulating through the thermo device.
Next,the cold start injectors can be checked for leaks( inside the manifold) by looking at the back of the manifold and you will see the cold strart valaves.there is a 10mm bolt ,undo this and turn on the igniton,there must not be any drips of fuel.
Thats about all you can safely check for...Waer seems to be around the govenor mech.in the back of the pump so theres not much show of adjusting it out.[xx(]
...There are old cars,and then there are Classics..(Mercedes Benz Ad. 1999)