CIS Diagnostic, help

[Steve Sherman]

A bit more info on my 86 5KTQW that won't start (or stay running the few
times it does catch)...

Starts/runs if you feed it ether.  Checked for vacuum/hose leaks, but
did not find any.  Spark plugs are sooty, from too much fuel not oil.
Good compression, and crank, valves and dist are all in sync. Fuel pump
works, but when I took a pressure reading, I got 40-50#'s; with quite
alot of jumping around (that is it did not settle down at a steady
pressure).  This is with the engine off and the fuel pump jumpered to
run.  And FWIW, the air plate in the fuel distributor seems hard to move
up, but comes down easily; up resistance goes away when fuel pressure is
removed.

I'm trying to add these all up to come up with a likely diagnosis, but
seems like they are pointing in different directions...  The low/erratic
fuel pressure would seem to say clogged fuel filter or bad pump.  But
the sooty plugs and up pressure on the air plate seem to point to too
high a fuel pressure.

Anyone in list land an expert on the CIS system?  Could low or erratic
fuel pressure cause rich running sometimes (sooty plugs) and no fuel
situation others?  Other possibilities that fit these symptoms?

TIA

Steve