Plagued by the middle and front-most SU carburettors "spitting back" (lean?), I consulted the manual and numerous YouTubes.
Released choke cables, took the RamFlow filters and carb tops off, ensured jets at the top of the seat then set down by ~4mm with the verniers (more or less the 3 screw turns).
Put back together and tested 4 times.- car ran worse - running on 2 cylinders and spluttering - disconnected plugs leads and only disconnecting #1 and #2 made much difference.
Then went back to basics - spark, compression, fuel.
Checked compression (150psi) and had spark at each plug.
So it must be fuel - I had overlooked the obvious!!!
Disconnected fuel outlet line at filter - just a dribble; inlet pipe was strong flow.
The car has been sitting for 15 yrs - I had cleaned the fuel tank, replaced the fuel filter but the new filter was completely clogged with muck that must have been in the lines.
So, enough fuel was getting to carb #1 but carbs #2 and #3 must have been starving.
Lesson learned - dont overlook the obvious!!!!!!!

 

It may be worth checking the filter from time to time as fuel lines don't flush easily and it can take a while for all the dirt to work it's way out.

 

Its going in for auto trans service on Tues - am going to get 2 filters!!

 

Remember if you remove the screen filter & insert a cartridge filter they clog from the inside out. Not from the outside in. You will see no debris in the glass bowl. Not to be confused with the burnt cake filter which I have never used. (not available in SA ~ I think they are available in the US as an AC Delco part for a tractor or whatever)

Cartridge filter.



Burnt cake filter.

 

You should have seen what was in it Glyn - yuk! Yes I made the mistake of presuming that I would see it. I replaced filter after I cleaned tank and tank filter - what was in tank was unbelievable. I ran fuel from the pump to the filter inlet into a container today. Seemed OK.
Traps for you players (I have had ~40 cars of different types but just an amatuer mechanic.