Brian,

     Your master cylinder is under the cover that is on top of your
instrument panel.  If you sit in your drivers seat, feel up front toward the
windshield & you will feel two indentations.  Pull up & back toward you
carefully & it will pop off.  There is your master cylinder.

     Pull your plugs & take a look at the color.  Check the gap.  Mileage is
affected by lots of variables.

Pat Callaghan
87 GL Westy
Portland, OR.
www.cybcon.com/~patcal