Hi Mike,
After various problems with dirty plugs, frequent stalling from low revs and smoke at high revs, I took my B20 to a specialist with a rolling road. It has a pair of Weber 40 DCZ 5 carburettors.
Whilst expensive to have done, it was well worth it and she has run much better since.
This may not necessarily help, as every car is different, but I ended up with these jet sizes:
Idle jets: 50
Man jets: 125
I am certain that others are much better qualified than me to help with this!
Kind regards,
Charles