I remember another fault that can *apparently* occur with these units.
The underside of the unit has a hole in it (some versions vary) so
that it is open to atmospheric pressure, and somewhere between the
unit and the mounting bracket, it gets blocked.

Inside is a bi-metallic strip that is heated by an electric coil as
well as by ambient temperature. The purpose of this strip is to push
against a spring, countering the effect it has upon a fuel valve port,
restricting the flow, and consequently affecting the system's control
pressure. When the strip is cold, the spring is restrained, and a
richer mixture results for cold running. As the strip warms up, it
moves away from the spring, which can then bear harder upon the valve,
reducing the mixture for normal running. Have a look here for diagrams
and further detail about K-Jet http://www.auto-solve.com/mech_inj.htm

If the strip doesn't lift off the spring retainer (for example, if the
heater coil has failed), the car will start normally from cold, and
then gradually behave as if the mixture was over rich. If the strip is
damaged, and is permanently away from the spring, it will be hard to
start, but behave normally when warm. If the valve port is blocked it
will be harder to start, and may show signs of a weak mixture when
warm. If the spring is weakened, then a permanently enriched mixture
will result.

In practice, the bimetallic strip doesn't move more than a few
millimeters, and this can be checked on the bench by opening the unit
and connecting the heater coil to a 12v battery.

I have repaired a warm-up regulator, but other than re-solder a broken
wire to the heater, you are very limited with what you can do. It is
possible to alter the position of the bimetallic strip inside by
whacking it's mounting post with a hammer (I've done it), but this is
hardly precision adjustment. Easier by far to replace.