[Mgs] Moss SU fuel pump

[Paul Hunt]

Originally the MGB fuel pump used capacitor quenching which was not polarity 
sensitive.  However it still resulted in some points burning, so a diode was 
substituted towards the end of production which was much more effective, but 
made them polarity sensitive.  These had an 'AZX' prefix.  Subsequently the 
diode was replaced by a metal oxide varistor or transient voltage suppressor 
which is not polarity sensitive, but uses the same part number as the 
earlier negative earth diode i.e. polarity sensitive pump.  Some sources 
still quote these as polarity sensitive, and even the supplier SU Burlen 
were confusing at one time at least as the box stated 'dual polarity' but 
the instructions inside stated 'All AZX pump are polarity sensitive'.  The 
only way to be really sure what you have is to remove the electrical end 
cap.  Diodes are black cylinders with one black and one red coming out of 
one end.  MOV/TVS tend to be blue discs with two wires the same colour.

PaulH.

----- Original Message ----- 
> Looking at the Moss Motors web site I see that the fuel pump that they
> list for the MGB is described as
> "Not polarity sensitive".  I know that the older ones had a diode to
> prevent arcing across the points which
> obviously made them polarity sensitive.  Any idea what the new ones are 
> using?