Atomiser -DELLORTO (type: 5353) SI-

The mixing tube (occasionally also called atomizer) of the SI carburetor has a big influence on the quality of the premix. The available pallet ranges from BE1-BE6. However, the name of the mixing tubes cannot be used to give a general idea of which type is richer or leaner. Depending on speed and load, the mixing tubes deliver different flow rates.

Function nozzle block SI

In the nozzle block area of the SI carburettor (depending on the filling level in the float chamber) there is always a defined fuel level available. I.e. below the atomisation tube (which opens into the intake area of the carburettor) 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 carburetor, but also ensure a higher level in the nozzle block area, which means that the premix can no longer work properly and possibly even fuel from the atomizer runs directly into the engine (sink). The actual problem is also not a too small volume of the Schhwimmerkammer but an e tuning over the air nozzle.

From the very bottom by means of the main nozzle the following petrol quantity is defined. In the middle is half in the gasoline, half in the air, the so-called mixing tube (e.g. BE3). From above, the air nozzle defines the air volume flowing in from above.

MIXING PIPE
The pre-expansion process in the mixing tube is very complex and strongly dependent on pressure/revolution. The mixing tube has various cross bores. These are partly in the petrol level, partly outside of it in the air range. Depending on the size, quantity and positioning of the bore, this results in different pre-expansion behaviour.

It should be noted that there is generally no lubricating or degrading mixing tube per se.
As a rough guide, it is therefore best to show a delivery characteristic curve in relation to the speed.

BE4 - BE6 - BE5 - BE1 - BE3 - BE2

In this list, from left to right, the mixing tube is rather greasy at low speed and thinning at high speed. The whole thing then tilts accordingly and becomes leaning at low speed and greasing at high speed.

Caution: The mixing tubes have an effect over a very wide speed range. A BE4 mixing tube, for example, already greases vigorously shortly above the idle slide position. A BE2, on the other hand, is relatively lean in the lower dehydration range, but greases strongly at the top.

The most commonly used BE3 mixing tube covers 90% of all SI carburettor applications. In addition, the gas slider used should also be checked here (see slider SI).

TIP

The combination of air nozzle 160 with mixing tube BE3 is sufficient in almost all cases. If the filter bottom is drilled and/or a resonance exhaust is installed, the mixing tube can be changed to BE2 and the air nozzle to 140 if necessary.

(US)

(machine-translated)