The basic Lambretta air filter is quite basically designed for basic engines; any increase in performance can cause restriction in air flow. Although there are a number of ways to help this, such as drilling air boxes, widening the air scoop and neck, the basic make up of a paper air filter can still restrict air flow.
This will cause problems in getting jetting correct as well as restricting performance. The main problem with the air filter box, is that air needs to be held in reserve, look at it as a being like a fuel tank, if there is not enough air in the box, when your engine needs maximum air, the air filter system cannot keep up and runs dry for want of a better word. We all fit fast flow fuel taps, but then neglect the air system. Also the nature of the paper air filter element is not the best method of allowing high air flow,
The are two other filters on the market other then the standard type. The first is a high flow item, still looking like the original filter, and still fitting within the standard Lambretta air box. The second is a remote filter; this normally involves using a Lambretta carb to air box rubber and bonding on a general purpose after market filter from companies such as K&N or RamAir etc to improve flow. Depending on your set up, jetting etc etc, tests we have done can see any thing from ½ to 2bhp more by switching air filter systems.
