Electronic Control Unit

The electronic control unit processes inputs from the oxygen sensor, ignition coil (engine speed), and choke. It is also connected to battery voltage and ground. An output signal is sent from the control unit to the vacuum regulator to control mixture ratio.

When the choke is pulled out, the control unit is in "Open Loop" operation. The vacuum regulator then operates at a constant 40% of maximum vacuum, which is 2.4 plus or minus 0.8 in. Hg.

When the choke is off, the system is in "Closed Loop" operation. The oxygen sensor signal is processed, and if it reads rich, vacuum increases to a maximum of 5.5 in. Hg. If the signal is lean, vacuum is decreased to atmospheric pressure.