Method for adjusting the air-fuel ratio of an internal combustion engine

An internal combustion engine comprising:

• a fuel supply section comprising a control unit for adjusting an air-fuel ratio of the engine;
• an engine throttle in communication with the fuel supply section;
• and
• the control unit for adjusting the air-fuel ratio configured to have a routine to:
• measure the engine speed of the engine;
• compare the engine speed to a first engine speed value;
• and
• adjust the air-fuel ratio if the engine speed is lower than the first engine speed value;
• said control unit repeating said routine until the engine speed is either greater than or equal to the first engine speed value;
• wherein the engine is crankcase scavenged such that at least a part of the air needed for the engine is crankcase scavenged.

A method for engine control comprising:

• running a test based control essentially defined by a brief fuel shut-off and a measurement of a number of engine revolutions in connection with the brief shut-off;
• adjusting a fuel amount based on the effect of the brief shut-off, the adjustment performed after an aggregation of a plurality of shut-offs;
• and
• combining the test based control with at least one of the following control methods:
• a free speed control method, an idle speed control, or a lean prevention control method;
• wherein the engine is crankcase scavenged such that at least a part of the air needed for the engine is crankcase scavenged.

Method for adjusting an air-fuel ratio of an internal combustion engine, in a fuel supply section, the fuel supply section comprising a control unit for adjusting the air-fuel ratio of the engine, the engine having an engine speed and an engine throttle ranging from zero throttle to full throttle, the method comprising the steps of:

• a) measuring the engine speed of the engine;
• b) comparing the engine speed to a first engine speed value;
• c) adjusting the air-fuel ratio if the engine speed is lower than the first engine speed value;
• and
• d) repeating the above elements a) to c) until the engine speed is either greater than or equal to the first engine speed value
• e) comparing the engine speed to a second engine speed value, the second engine speed value arranged to be larger than the first engine speed value;
• f) adjusting the air-fuel ratio if the engine speed is higher than the second engine speed value;
• and
• g) repeating the elements a) to step f) until the engine speed is in the range of the first and second engine speed values.

Method for adjusting an air-fuel ratio of an internal combustion engine, in a fuel supply section, the fuel supply section comprising a control unit for adjusting the air-fuel ratio of the engine, the engine having an engine speed and an engine throttle ranging from zero throttle to full throttle, the method comprising the steps of:

• a) measuring the engine speed of the engine;
• b) comparing the engine speed to a first engine speed value;
• c) adjusting the air-fuel ratio if the engine speed is lower than the first engine speed value;
• and
• d) repeating the above elements a) to c) until the engine speed is either greater than or equal to the first engine speed value;
• wherein the engine uses a rich fuel setting when started, the rich fuel setting providing a rich start air-fuel ratio that is richer than a first engine air-fuel ratio corresponding to the first engine speed value.