Air corrector jet -DELLORTO (type: 5827) SI- (120)

The air jet (exactly: main air correction jet) of the SI carburettors has a great influence on the amount of air supplied to the premix. The available range is from 120-190. 120 air jets have a bore of only 1.2mm, so they provide very little air and are greasing accordingly. A 190 air nozzle provides a lot of air and is therefore very lean.

function nozzle block SI

In the nozzle block area of the SI carburettor there is always a defined level of fuel (depending on the level in the float chamber). I.e. below the atomizer tube (which opens into the intake area of the carburetor) there is a petrol column. For this reason we also advise against the so-called float chamber spacers. These increase the filling level in the carburettor, but they also provide a higher level in the nozzle block area, which means that the premix can no longer work properly and possibly also petrol runs directly from the atomiser into the engine (spillage). The real problem is also not a too small volume of the float chamber but a tuning via the air nozzle (see below). In the middle is half in the petrol, half in the air, the so-called mixing tube (e.g. BE3). From the top the air nozzle defines the amount of air flowing in.

If the air nozzle is too large (e.g. 190) no sufficient negative pressure can be formed and the fuel supply under full load is dangerously leaning or breaks down completely (often confused with sucking the float chamber empty). In this case, even raising the main jet is of limited or no help at all.

This phenomenon also frequently occurs with modified standard air filters, where the hole drilled over the air jet is too large for the engine's requirements (e.g. 8mm).

The same happens when using Polini or Pinasco air funnels instead of the air filter. In order to compensate for these modifications, not only the main nozzle has to be considerably larger, but also a smaller air nozzle has to be used (e.g. 140 instead of 160).

TIP

Series engines with series filters can usually always manage with a 160 air nozzle. Tame tuning variants such as a Pinasco 213 can also be operated with the lean 190/BE4 combination (original PX200 10HP variant) (but then never combine with a modified air filter). An engine tuning with a lot of power may also need an air nozzle with only 140 or smaller to avoid a lean one under full load.

(US)

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