Marcos Maniacs

Hello Martin
The  pattern on my 71 Volvo 3 litre powered Marcos is 3.75 pdc with four 
7/16ths  studs.
I am guessing that your fathers car has the same induction set up as mine,I 
also to have hade a little trouble adjusting the idle ,it ticks over ok now 
but does smell a bit rich.If you do change to the triple carberator or an 
injection system please let us know how things go.
Good luck .Mark