My 1990 Domino 850cc has always run a trifle on the rich side and since I cannot obtain any sort of workshop manual, I have left well alone. The other day I checked the condition of the air filter element and was somewhat horrified to find that the filter had been shedding what looked like fine glass or ceramic fibres, which were being gobbled up by the carb and were stuck all around the intake orifice. Air filters are rarely cheap, so rather than changing it for yet another useless obstruction in the airflow, I converted to nylon stocking filters, which had worked so well on a variety of cars in the past. First obtain your stockings or tights ( could be fun ). Cut a generous unladdered section ( double thickness ) and stretch over and securely ( very secure with no risk of being sucked in )attach to the end of the air intake hose with a plastic strap. Do the same for the other intake hose which is only in use on the "winter" position ( you can chuck the old winter flexible if you wish). Make sure the ends of these inlet hoses are not obstructed and that any bends are as gentle as possible. Remove and discard the airfilter element but retain the air filter box assembly because this acts as an effective "cold box". Screw the lid back on ensuring that seals are good and the arrows on the lid and body line up.
Nylons breathe so freely that you may find that you have to slightly richen your mixture to suit although my carb was already over rich. The nylons will not be as effective at trapping fine dust as a regularly changed filter element, so I would not advise this mod if you live in a very dusty area or go dune bugging. However, in my relatively clean area I used this filter arangement on a road tuned Midas 1275cc ( A Series Leyland engine) in which I completed over 170,000 miles without undue engine wear.