4k wont start

[wls11 at scasd.k12.pa.us]

hey all, hoping someone can help me with my latest no-start 
problem. patient is a 1981 4000 5+5 with the WE 2144cc 5-cyl. 
Last sunday, i took all of my plugs out, cleaned them with a wire 
brush, re-gapped them.  Monday morning--car runs smoother than 
it has in a long time.  Drive home from school in the afternoon--fine. 
 Leave for the pool in the evening--starts, but then dies, and wont 
start--spins, catches, but then dies.  i get home two hours later, 
starts up fine.  Next day (tuesday) starts fine to go to school, still 
running smooth as ever. after school, wont start at alll (no catch, 
still spins), and wont start a couple of hours later when i go back to 
check it out (no catch, still spins).  This evening, just a couple of 
hours ago, starts up fine, runs smooth.  Drive to gas station, as 
tank was low, and possible culprit.  Fill tank, then same result as 
monday--spin, catch, but then dies.  If it will start tommorrow, it is 
going to my mechanic.  Very similar symptoms last spring were 
cured with new rotor and cap, spark plugs, and fuse board.  if it 
matters, I installed new speakers in my front doors on sunday, 
also, but the wiring had been in place for a couple of weeks.  Any 
suggestions would be appreciated, as i am getting sick of getting 
stranded, and this is confusing--when it runs, it runs very smooth 
(though my reference is a TDi Passat), and doesnt seem to be hot 
or cold start specific.
Thanks in advance
Bill Serencsits
1981 4k 5+5 201000mi
wls11 at scasd.k12.pa.us