For homebrew, working on motorcycles, always up to date selection of the optimal variant of the air filter. The most common available contact-oil (lubricated with a thick oil mesh or nylon “thread waste”) and paper (automotive type) filters. Last predpochtitelno: they provide a high filtration rate (up to 0.98) and low resistance to air flow, but their dimensions are very significant.
A few years ago when you next upgrade your motorcycle “IZH-JUPITER 4” I installed two carb and long suffered in search of a suitable filter: a “native” without substantive alteration does not fit.
I saw in the store stepped rubber coupling (to connect the drain of the toilet), estimated by eye the size: like fit to paper filter from engine moped /-50. And so it proved. Smaller neck of the rubber coupling with interference sets in the inlet of the carb, for a secure connection you can pull the screw clamp. Inner diameter larger neck makes it easy to install moped filter (diameter — 74 mm). To increase the density of the region of the coupling emptied out the car and squeezed the clamp (photo not shown). The hole in the outer end of the filter is choked with a rubber washer using the M6 screws. Screw — out .