What does a Lambda Sensor measure?

Lambda Sensors were developed for the electronic control of modern internal combustion engines. They measure the residual oxygen in the exhaust gas and thereby indicate whether an engine is running too rich or too lean.

At a lambda value of 1.0, complete combustion theoretically occurs. This corresponds to a ratio of 14.7 parts air to 1 part premium gasoline. If the AFR value is higher, the engine is running leaner. If it is lower, the engine is running richer.

Advantages for Carburetor Tuning

In recent years, more and more Vespa riders and dynamometer operators have come to appreciate the benefits of Lambda Sensors. With these Replacement Parts, guesswork when adjusting the carburetor is a thing of the past. Whether the engine is running too rich or too lean can be read directly on the display.

Especially on long trips or during extended periods of full throttle, it provides a much greater sense of security to be able to verify that the engine isn’t running too lean.

Connection to the SIP Speedometer/Rev Counter

The SIP A/F Converter allows you to connect a Lambda Sensor to the SIP Speedometer/Rev Counter. The temperature sensor connection is used for this purpose. Instead of Cylinder Head or outside temperature, the display then shows the AFR value (Air Fuel Ratio).

Example: A reading of 147 corresponds to an AFR of 14.7. A reading of 160 represents an AFR of 16.0 and thus a leaner mixture.

For performance-oriented carburetor tuning, AFR 14.7 is not the ideal value; instead, a slightly richer mixture is usually preferred. A lambda value of approximately 0.85, or an AFR value of about 13.5, also benefits the engine’s internal cooling through the fresh air-fuel mixture.

If the A/F Converter is connected to the SIP Speedometer/Rev Counter, a temperature sensor cannot be used at the same time.

Installation in the Exhaust System

Detailed Mounting Instructions are included. On newer SIP PERFORMANCE racing exhaust systems, the Lambda Sensor can be screwed directly into the welded-on lambda sensor nut.

For exhaust systems without an existing connection, suitable weld-on nuts or flange kits are available and must be ordered separately. Depending on the exhaust system, be sure to select the appropriate version made of steel or stainless steel.

Power Supply and Operation

The wide-band Lambda Sensor is type LSU 4.2. Wide-band Lambda Sensors are heated and require a powerful power supply. We recommend a SIP PERFORMANCE Ignition system connected to a Battery.

The current draw is approximately 1 A, and during the warm-up phase it can even reach approximately 3 A. A Battery in the circuit is therefore recommended.

Although it is often claimed that Lambda Sensors are not suitable for use in 2-stroke engines, we have had ample experience to the contrary. If the Lambda Sensor is not used for an extended period and the vehicle is operated with a very rich mixture, it is advisable to remove the Sensor from the exhaust system to protect it.

Guideline Values

• Lambda 1.0: stoichiometric combustion
• AFR 14.7: 14.7 parts air to 1 part fuel
• AFR above 14.7: lean mixture
• AFR below 14.7: rich mixture
• AFR approx. 13.5: useful guideline for performance-oriented tuning

These products are a perfect fit – SIP TIPS:

• To seal the lambda sensor connection in the Exhaust , be sure to order the Lock Screw (including Gasket) at the same time. With the SIP flange kits, part nos. 50412700 and 50412800, virtually any Exhaust system with a lambda sensor connection can be retrofitted.