Hay, goodONya dude!!  
  I hope it's a good one.  When I bought my '76 it had only an electric
pump such as you describe.  It also had a Z-S carb that ran so rich it
fouled the plugs in short order.  I put a new mechanical pump on it
because I wanted to be sure the fuel pressure to the carb was correct. 
I use the electric as a boost pump, with a toggle switch, to fill the
carb before starting after it has been sitting for a few weeks.  The car
is still a work-in-progress, y'see.  Also keeping the electric is good
insurance, IMHO.
  Cheers,
   CR
///
///  (If they are dupes, this trailer may also catch them.)
 
 |