the problem i have is that my car (88 EA Ford Falcon) runs rough when i
start it after i have left it standing for about 8 or more hours.

I can start it but for about 10 mins below 2000 to 2500 rpm it runs really
rough however once i hit/pass the 2000 to 2500 mark it runs fine until i
drop back below that rpm level.

This only happens when the car has been off for 8 or more hours.
I have already put injector cleaner through it which had no effect.
The plugs were supposedly changed when it had a full service so that should
be theoretically ruled out.

The car has a 3.9L engine with a 3 speed gear box and runns using duel fuel
CPI not MPI.
If anyone has any ideas i would be greatly appreciative.