Carbureted Harley motorcycles pass EURO-3 exhaust test with the AMM-L1 Precision Valve.


2014: ZEROENGINEERING chooses AMM-L1 for their new Type-6 motorcycle. The Type-6 (shown below) features 1520cc S&S Shovelhead Carburetor Engine. According to Zero's president Toshio Matsushima the Type-6 has already been marketed in Japan and will now be available in the EU.


In February 2007 Rinke Andringa, head of New Rebel Motorcycles who is the European distributor for Saxon Motorcycles has the world's first carburetted motorcyle that passes the EURO-3 exhaust test. It uses the AMM-L1 precision air valve for lambda regulation.

The engine is a Evo-style S&S with 96 cui, and is fed by a Mikuni HSR 42 carburetor.

In November 2007 Anton Aalders, CEO of Climax Motorcycles adds on to that success:

His bike passes EURO-3 with a S&S 113 cui engine (about 1850 ccm), Mikuni HSR 42 carb and AMM-L1 Precision Lambda Valve with excellent exhaust values, that are significantly lower than those required by the EURO-3 norm.

More examples will most likely follow in the near future, however it is already shown, that a carburetor that is equipped with the AMM-L1 Precision Lambda Regulator can achieve equal or even superior exhaust performance, compared to todays fuel injection systems.

And you seem get there much easier ;-)



The AMM-L1 is a precision air valve that can be used for Lambda-Control in any carbureted engine.

Working Principle

Lambda- (oxygen) control in combustion engines is today performed as a fuel-mass regulation controlled by the complex electronic injection system with the input of a Lambda-(oxygen)-Sensor, residing in the exhaust pipe.

Principally the same can be done - in a much simpler fashion - with any carburetted engine with the difference that not the fuel-mass is regulated, but the amount of air that is mixed with the fuel.

As the proper setting for any carburetor is to be slightly fat in all operating conditions, all that has to be done is to add some air after the carburettor in order to lean the mixture and make it exactly stoichiometric, which means that the match of fuel and air is such, that a perfect and complete combustion can occur.

This task is performed by the AMM-L1 Precision Air Valve:

It reads the signal from a standard Lambda-(oxygen)-Sensor. If oxygen-sensor says "fat" the AMM-L1 Precision Air Valve gradually opens a by-passage, leaning the mixture, just until the sensor says "lean", then the AMM-L1 gradually closes the air by-passage. This way, the mixture is adjusted to Lambda=1 under all operating conditions.

A green LED (a separate LED can be optionally mounted to your dashboard) displays the mixture status: ON = fat, OFF = lean.

As the AMM-L1 Precision Air Valve will always adjust the mixture for optimum combustion, the green LED will flash on and off almost all the time. If it stays ON or OFF at certain throttle positions for more than a couple of seconds, you know that your carb is too fat (respectively lean), and needs to be adjusted.

In conjuction with a catalytic converter the AMM-L1 Precision Air Valve achieves 3-way catalytic conversion on any carbureted engine and is an easy way to upgrade existing engines to drastically reduce exhaust emissions.

The AMM-L1 Precision Air Valve is also a valuable tool to determine perfect carburetor adjustment and it will constantly fine-tune the mixture for optimum combustion. Btw. a carburetor that has been adjusted with the help of the AMM-L1, will also run perfect with the Air Valve disabled (closed), however mixture will then not be fine-adjusted as lambda-regulation is not performed.

Please take a look at the AMM-L1-system-overview.pdf.

See below a high-performance motorcycle carburetor (S&S Super B). The AMM-L1 precision air valve meters air/fuel ratio by gradually opening a bypass between the air-filter (left) and the intake manifold (right). A fat mixture (monitored by oxygen sensor) will enlarge the bypass diameter, while a lean mixture will reduce the bypass diameter or even close the valve completely.

Why Lambda Control ?

Lambda-control has an advantage when used in combination with a catalytic converter. The conversion rate is raised, in other words: the catalytic converter can do a much better job in reducing exhaust emissions compared to an engine without lambda-control.

See below a single-wire NGK / NTK oxygen / lambda sensor and the AMM-L1 precision Lambda Regulator mounted to a Harley-Davidson Softail motorcycle with stock catalytic exhaust pipes.

See below the valve and electrical connections: Plus (from ignition switch), frame ground, oxygen sensor and auxiliary LED output.

Please take a look at the AMM-L1-electrical-connection-diagram.pdf

Why Catalytic Converter ?

The catalytic converter is a tool to make the exhaust gas resulting from the combustion of gasoline (petrol) and air less harmful, as it can convert poisenous gases like CO, NOx and HC to harmless gases CO2 and N2 (which are already in air) plus water (H2O).

As a downside one should be aware that during the manufacture of catalytic converters large amounts of poisenous gases are blown into the atmosphere, so that the net-result of the catalytic converter itself is reduced. Additionally the catalytic substances platin, palladium and rhodium, as well as ceramic fibers, gradually leave into the atmosphere during the lifetime of the catalytic converter, also entering ground water, plants, etc.

Lambda Regulation and Idle

Stability and adjustability of idle rpm is necessary. While Lambda-regulation is not a problem at all for idle speeds of 1000 rpm and higher, it can be a challenge for engines that are desired to have a significantly lower idle speed. Therefore AMM-L1 Precision Lambda Regulator has a switch input. An optional idle switch can be connected to the AMM-L1 module, which will give contact when throttle-valve is closed (for idle) and the AMM-L1 valve will close its air passage immediately, allowing for a very stable idle adjustment. As soon as the throttle is moved above idle, the AMM-L1 valve will resume its Lambda regulating operation.

Take a look at the AMM-L1-connection-diagram-with-idle-switch.pdf

System Integration

The AMM-L1's miniaturized electronic control unit includes a microprocessor, stepper motor control, A/D converters, reverse polarity protection and additional features. It has been integrated into the stepper motor, so that you do not need to install a seperate blackbox and associated wiring. The complete AMM-L1 assembly is protected against moisture and humidity.

Compatibility and Options

The AMM-L1 Lambda Regulator can be used with any carbureted engine. You can use heated or unheated oxygen (Lambda) Sensors of different manufacturers. We have tested with NGK / NTK Sensors. Please specify if you want to use Zirkonium-type (standard) or the newer Titanium dioxyde also referred to as "Titania"-types, which requires a slighly different control board. Other manufacturers of Lambda (oxygen) sensors are Bosch, AC/Delco and Delphi.

Prices and Package contents

The AMM-L1 High-Precision Lambda-Regulator comes EUR 500,- incl. shipping to your location.

The package contains:

1 x AMM-L1 Precision Lambda Regluator (which is an assembly of the valve body, stepper motor and electronic module)

1 x idle switch (that you can use optionally if you need low idle)

1 x green LED (which you can mount to your dashboard)

1 x threaded fitting, 3 pipe fittings (to accommodate different size engines), all fittings are standard pneumatic G1/4a thread.

What you supply

The Lambda Sensor is not included in the package. You also need a couple of rubber hoses and wires. For some installations a G1/4a thread tapper is required.

You must be familiar with your type of engine and carburetor used. You must have certain electrical and mechanical skills and understand the basics of combustion, air/fuel mixture and Lambda Regulation.

If you have any questions concerning this product, please use the below email address.


ALTMANN MICRO MACHINES ... Dipl.-Ing. Charles Altmann ... Erlenstr. 15 ...42697 Solingen ...Germany

phone +49-212-233-7039 ... email


disclaimer: Terms marked with ® may belong to the Harley-Davidson factory, which is in no way affiliated with AMM.