I have finally got round to having a go at adjusting the Weber. It has always seemed sluggish at low RPM and the plugs are always fairly black although I have done very few miles on it as I am only occasionally re-united with the bike. I have now adjusted the float height to 42mm. I don't remember what it was previously but it was greater than that.
When I read the manual it suggests (as does the diagram) that the air adjusting screws are higher (towards the petrol tank) than the idle mix adjusting screws. From the diagram these are the ones that can reached with the air filter in place. Indeed the idle mix adjusting screws seem to be the ones that are at 45 degrees to the carb. Once the air filter box is on it is impossile to adjust what it calls the idle mix screws unless the air filter element is taken out and the rubber caps are removed. This would make a mockery of setting the idle mix. Is the manual wrong and has confused which is which.
Once I know which screw is which I will let you know how many turns mine were out.
Thanks.

OK I have spent ages looking at pictures of Webers and it seems that the manual is right and I was wrong. So it appears that I can access the air adjusting screws to balance my carb with the air filter in place but to adjust the idle mix I have to take the air filter element out remove the 2 plastic plugs (are these the inviolability caps referred to in the manual) and adjust the idle mix with no air filter. This doesn't make sense to me and I am cleary missing something here. Anyone able to enlighten me.
Incidentally my air adjusting screws were both open 1/4 turn. Obviously one should be closed. The idle mix screws were both out 2 turns. As I said in my first post the mixture appears quite rich.

A very good place to start

Have a look to my tips in 750 FAQ about tuninig and balancing yur carb.

Thanks for your help. Carbs balanced at tickover and checked at higher RPM and they were still in sync. Idle mix screws were fine although having been brought up on old British bikes with Amal carbs I stil find it odd that it has to be adjusted with the air filter element out.