as above... start with the correct springing for your weight and try diffrent grades of fork oil
But putting spring spacers in rubbish forks.. just makes harder sprung rubbish forks..
the damping is not able to control the standard springing... So putting preload spacer in only makes the damping less effective..

Gold valves & the correct springing for your weight...
Or
fork replacement with the correct springing for your weight..

not sure what the hot set up for a motad is..
dirt... 35mm static sag / rider sag 33% of travel.
Road... 10mm static sag / rider sag 20% of travel..
So Motad could be somewhere in between..??????

If yer get the front sorted... you will then notice just how bad the rear shock is...

__________________
Harley Davidson..
The easyest way to turn gasoline into noise with out the side efect of horse power...