Description

Air Filter SI 20.15-20.17

MADE IN INDIA

Fine filter
This Indian version has double filter fleece for a long engine life.
If this filter is used the jetting should be reduced accordingly, since the throughput is clearly smaller compared with a standard filter.

short version
Only usable on the small old SI carburettors like 20/15 or 20/17 (e.g. VBB or similar)

Description
A peculiarity of the SI carburettor is the fact that it is difficult to tune without an air filter. It reacts sensitively to changing pressure conditions.
This has to do with its mode of operation as a downdraft carburettor, where the nozzle block is supplied by a so-called main air correction nozzle.
A hole is often drilled in the filter bottom above this nozzle to improve the air flow to the air nozzle.
This measure usually improves the pre-foaming, but with heavily modified engines it can lead to a too low negative pressure in the nozzle block.
As a result, the fuel level drops below the threshold of the atomizer/petrol outlet tube and the engine is only insufficiently supplied with mixture.
Apart from a too lean full load operation, which usually no larger main nozzle can catch, in extreme cases it can also come to a complete stop of the fuel delivery.
This often leads to the assumption that the float chamber was sucked empty.
This is usually not the case (assuming a proper fuel supply through an appropriate fuel tap), but merely a matter of adjustment via a smaller main air correction nozzle.
Differences of the SI filters

Fits the following vehicles