I found a sort of helix in a carburetor of a Briggs and stratton 5HP. The helix is inserted at the output of the carburetor. 6 cm long for a 180° rotation. It was a tight fit in the carburetor body.
Unfortunatly, the TD inlet pipe is not long enough.
Not possible to insert picture ?
I would assume this is intended to introduce swirl into the mixture. Its purpose will be similar to that of the neublizer we fitted for the test. Althoug I suggest it will not be as effective or reduce the high RPM power as much. The fact that similar spirals have not been used on other carburettors suggests it probably did not offer any benefits at the time.
However, with the effects of modern fuel, it may give some improvements.
If anything is fitted into the inlet manifold, it needs to be very securely fastened otherwise it may get drawn into the cylinder.