To reduce response delay of engine rotation speed to throttle opening operation in the increase or decrease control of engine rotation speed by changing over ignition timing at a predetermined rotation speed in an engine for a working machine not including a governor mechanism.
Engine rotation speeds for changing over ignition timing are set to 4,000 rpm and 5,000 rpm. Ignition timing is advanced stepwise from first ignition timing to second ignition timing to change over to rotation control characteristics C30 for high speed rotation during throttle opening increase. Ignition timing is retarded stepwise from second ignition timing to first ignition timing to change over to rotation control characteristics C05 for low speed rotation during throttle opening decrease. Change over timing of rotation speed control characteristics is different between the throttle opening increase decrease, but difference can be limited to small quantity ΔTH.
Michito Hiraki
Sanji Tanabe