If it chugs and misfires when you start it, and it belches out smoke it's probably the glow plugs as S/F says... If you remove the glow plugs, they are easily tested.
Get a short length of wire and attach it to your positive terminal of the battery.
Rest the threaded part, of the body of the plug, on the negative terminal.
....Dont put your fingers near the tip of the plug...you may get branded...!
Then take the wire and touch the end of the plug...where the power supply attaches.
It should glow inside a few seconds...
If it does'nt...it needs replacing.
I replaced one of mine last week...same problem..lots of smoke and a misfire, clearing up after a few minutes.