1975 280Z: different starting issue

I recently restored the fuel tank because rust was blocking the fuel line, resulting in the obvious problem.  But I am still occasionally experiencing a combustion problem.  My engine has cut out on me twice while driving.  I also had problems starting the car last night and this morning.  The engine turned over as it should, but I wasn't getting combustion for a couple minutes.  With a bit of persistence, the engined eventually roared to life with an excessive amount of grey smoke coming out of the tail pipe for 30-45 seconds.  The car now starts and drives, but for how long?  

Any thoughts/advice regarding likely problems and solutions?