Operating a dual fuel engine system includes igniting a main charge of gaseous fuel in response to combustion of an early pilot shot of liquid fuel and production of a spark. Operating the system also includes covarying a spark timing parameter and a pilot shot delivery parameter, and reducing an error in a phasing of combustion of another main charge based on the covarying of the spark timing parameter and the pilot shot delivery parameter.

Operating a dual fuel engine system includes igniting a main charge of gaseous fuel in response to combustion of an early pilot shot of liquid fuel and production of a spark. Operating the system also includes covarying a spark timing parameter and a pilot shot delivery parameter, and reducing an error in a phasing of combustion of another main charge based on the covarying of the spark timing parameter and the pilot shot delivery parameter.

A handheld engine-driven working machine comprises an internal combustion engine and an ignition control device; wherein the ignition control device can switch its control between a normal mode and a operation mode, wherein during the operation mode, the ignition timing within the high speed range is maintained at a second BTDC angle, and the ignition timing within the medium speed range is advanced more than a third BTDC angle between a first BTDC angle and the second BTDC angle, and wherein at any rotational speed within the medium speed range, the ignition timing during the operation mode is advanced more than the ignition timing during the normal mode.

An engine kill switch and a throttle lever position sensor switch both remote from the engine and connected by a pair of wires to a microcontroller for controlling a spark initiated combustion of an air-fuel mixture in a cylinder of the engine. The switches may be received in the same housing and mounted in an operator handle housing of a hand held power tool.

An engine kill switch and a throttle lever position sensor switch both remote from the engine and connected by a pair of wires to a microcontroller for controlling a spark initiated combustion of an air-fuel mixture in a cylinder of the engine. The switches may be received in the same housing and mounted in an operator handle housing of a hand held power tool.

A handheld engine-driven working machine comprises an internal combustion engine and an ignition control device; wherein the ignition control device can switch its control between a normal mode and a operation mode, wherein during the operation mode, the ignition timing within the high speed range is maintained at a second BTDC angle, and the ignition timing within the medium speed range is advanced more than a third BTDC angle between a first BTDC angle and the second BTDC angle, and wherein at any rotational speed within the medium speed range, the ignition timing during the operation mode is advanced more than the ignition timing during the normal mode.