Dellorto, an Italian carburetor manufacturer, measures fuel jets differently from other manufacturers because of the unique design and calibration standards they use for their products. While many carburetor manufacturers use a universal numbering system to indicate the size of the fuel jets, Dellorto employs its own system based on the flow rate of fuel through the jet.

Dellorto's fuel jet sizing is determined by the flow rate of fuel in grams per hour that can pass through the jet when there is a pressure difference of 0.15 bar (approximately 2.18 psi) between the fuel inlet and outlet. The jet size number corresponds to this flow rate value, whereas other manufacturers often measure the jet sizes by the diameter of the orifice in millimeters.

The main reasons for this difference are:

Design philosophy

Dellorto carburetors are designed to provide precise fuel metering and atomization for a wide range of engine applications. Their unique jet sizing system allows them to achieve optimal performance and tuning characteristics for various engines.

Calibration

By using a flow rate-based system, Dellorto can more accurately adjust the fuel delivery in their carburetors to suit different engines, ensuring a more precise and efficient combustion process.

Compatibility

Dellorto carburetors and their corresponding jets are often not interchangeable with other brands' products, which means they need a unique measurement system to maintain compatibility within their own product range.

While the jet measurement systems used by Dellorto and other manufacturers may differ, the ultimate goal is the same: to provide accurate fuel delivery and optimize engine performance. However, this difference in measurement systems can make it challenging to directly compare Dellorto jets with those from other manufacturers.