Maybe because they rarely fail or give a problem, we tend to ignore the
injectors in our engines.  Maybe we should think about them more often.  The
following is why I say this.
I just had an interesting experience with my '90 Westy, stock 2.1L WBX,
heads by PO at 88k, now just under 125,000 on the clock.
A little background.  For some time I had what felt like a partial miss, if
there is such a thing.  On acceleration it felt like one cylinder was not
quite doing it's share of the work.  Firing okay, but not providing the same
amount of work/push that the others were.  Compression test showed all
cylinders within 20% of each other, the usual criteria for thinking about a
valve job.  And virtually no oil consumption, half a quart in 1,000 miles.
This nagging problem was best felt when on the highway.  If going up a
slight hill a small vibration could be felt in the steering wheel.  Let off
on the gas and the vibration went away.  The passenger could not hear or
feel it.  Everything had been replaced in normal maintenance, plugs, cap,
rotor, plug wires.  The only thing that had not been messed with was the
injectors.  So I acquired a set of used injectors, had them rebuilt, and had
them put in last April, just before taking off for SDM. New plugs at the
same time, the Bosch quad point type, same as I had been running for four
years. The Westy  ran fine and I was convinced that the miss/hesitation had
gone away.  But one of the injectors went bad after about 150 miles.  In the
process of isolating the problem and fixing it the shop replaced one plug
with the standard Bosch single electrode plug and a used injector they had
on the bench.  Ran fine, but the miss/hesitation was back.
Running with three recently rebuilt injectors and miss matched plugs didn't
seem to hurt anything but was intellectually disturbing.  The shop that
rebuilt the injectors was very apologetic and even rebuilt two more
injectors for me for free.  Two days ago I replaced the 'off the bench'
injector with one of the rebuilt injectors (actually replaced both on that
side, they were already set up on the mounting clamp) .  And I replaced all
the plugs so that they matched, this time with the triple electrode Bosch
plugs.
Well, I've driven about 50 miles now, city and freeway, and the miss is
really gone!!  No hint of it.  This implies to me that my problem was in the
injectors, one not performing like the other three.
I'm leaving tonight on a three week trip, a couple of thousand miles by the
time I get home.  If all continues well (or if not) I'll report to the list
the results.
In the mean time, maybe we should pay a little more attention to having a
set of injectors that are matched, all providing the same flow rate.