A Buddy Needs HELP

My friend has a Spitfire  ...ZS carb, 12 volt coil, lucas electronic
Ignition, Ign Module AB14....heres the problem...and PLEASE ...I know.. its
a Spit.  OK.. Under acceleration runs fine...when cruising at any speed it
has a hestiation and miss.....it is 8 degrees retarded right now...says even
if advanced still has miss....while cruising if accelerating again...smooth
as can be ....I think its a timing problem ..but he says he has tried that
...any ideas????Thanks
Jerry G
59BE