Presuming the engine is piston ported, a good starting point for pilot jets would be in the low thirties.
If you don't already own them, a set of jets from the likes of Stage6 etc can be had @ very reasonable cost.
Before i can offer any further advice, what main jets & needles do you have available?
IMO these carburettors work extremely well on Lambrettas with adequately sized air filters, though they should be thoroughly checked prior to use, as is the case for any carburettor. I'm guessing you intend the use of an OEM type air filter set-up which should be fine if the box is of the bulging later type. PWK's have a good inbuilt overflow but lack an inbuilt fuel filter. You might want to consider augmenting the tank only filter with an inline filter & these are good & cheap:
https://www.gsfcarparts.com/121aa0010?a ... 4AQAvD_BwEThankfully, there is a load of information on the internet & this is easy to understand:
http://www.mid-atlantictrials.com/Sales.htmlDefinitely the float setting is essential but I've done a few of these carburettors now & find them intuitive to set. That said, I always remove any float stops within the bowl & carefully modifiy where the drain plug screws in to allow a screwdriver to access the pilot jet without the bowl removal.