You got the same engine that my car. (Jetta 90, 1.9TD from a Golf 94).
If the smoke is only at WOT (Wide Open Throttle, full acceleration) Don't worry about that. At the next timing belt change, the mecanician will adjust the pump timing. If you worry about that, get the car to a mecanical diesel who have a dial indicator with the VW 2206 (Id think, not sure) to adjust the injection pump timing to the desired value, (normaly near 0.90mm to 1mm is a good value for performance).
Or if you want more performance, install a boost gage (about 20$, piping, pool gage include) and adjust the wastegage to get more boost, you gonna get rid of the smoke and have more power. Adjust the wastegate lever to about 12 to 15 psi at WOT. I wish you doesn't have the Garrett T2 like me, is a pain in the ass to adjust(under the car, and very hard to turn the adjustment in the rust).
Smog DIY for the Injection Pump Adjustment and the Turbo Wastegate Adjustment. (French):
http://www.vwquebec.ca/forum/viewtopic.php?t=4344You can translate it with BabelFish (
http://www.altavista.com)
Where are you located ? i could adjust it for you.