You should be able to get a refurb kit - Burlen in the UK for example.
http://sucarb.co.uk/?SID=c8fijq3g6c4dlo136f5a0eteq0

If the float chambers are leaking, and the levels vary it will mess up the mixture, and possibly the fuel may be aerated. So fix that first. You may also find sludge in the float chambers.
New needles and jets will make a difference.

You might consider replacing the carbs, but refurbing is very satisfying!

DaveW
'05 Red Roadster S1
'16 Yellow (Not the only) Narrow AR GDI Plus 4