How and when to replace the atomiser-holder nozzle of the float-bowl carburettor on your kart (the practical 3-step guide for the kart driver!)

Introduction

In float-bowl carburettors, the atomiser holder (which some DELLORTO technical manuals also describe as the atomiser nozzle) is the insert positioned inside the Venturi. The atomiser screws into it, and the tapered needle moves along its internal channel. Its job is to set the atomiser in the airflow and create the pressure drop that draws fuel from the main circuit. Where the atomiser holder sits, and how it is fitted, directly affects how the carburettor picks up fuel — and therefore how the engine responds. This is why certain questions inevitably come up: Does it need to be replaced? When is it really worth doing? And how do you change an atomiser holder properly? In this article we answer each of these points, explaining in which situations replacement may be necessary. One thing should be made clear from the outset: changing the atomiser holder is not part of routine carburettor adjustment. It is a delicate and rather uncommon operation, because the insert is press-fitted into its seat, and applying the wrong force can permanently damage the carburettor body. For this reason, dedicated tools are essential — tools designed to guide the insert into position without distorting its seat. In the next slides we will look at which ones are used and how to handle them correctly. The procedure shown here — demonstrated on a DELLORTO VHSH 30 carburettor (used on Shifter engines in the FIA Karting KZ and KZ2 classes, and in the ROK Cup By Vortex single-make series; for more details see “Under Review | The DELLORTO VHSH 30 carburetor”) — is presented in a three-step guide.

Above, the atomiser-holder nozzle, which is interference-fitted into the carburettor body to ensure stable and precise fuel flow. Below, an atomiser-holder nozzle from a DELLORTO VHSH 30 carburettor.