As long as its black then its better then white or blue! But yes it does sound like a timing or ignition problem. I'd start with checking the timing.
1. Remove upper timing cover (should be 5 10mm bolts ones in the center of the timing cover so make sure you get it)
2. Remove all spark plugs (leave them attached to the plug wires and unplug the ignition coil!!)
3. Get a breaker bar and appropriate socket and slowly turn the engine over (its going to be tight with the fan and shroud installed but it is do able)
Here's a guide through the timing process:
http://www.cygnusx1.net/Supra/Librar....aspx?S=EM&P=7
If still in doubt about timing, remove your distributor cap and check the position of the distributor rotor, for proper timing it must point DOWN at #1 cylinder.
This should tell you everything you need to know/look for. Let us know if you have anymore problems.