Perkins 1606A Engine Running Slow
The Perkins 1606A engine has an input for speed control (AP1). By default this is ENABLED. It therefore requires a positive signal to DISABLE the AP1 input and the engine will then run normally at 1500 RPM.
Alternatively you can fit a potentiometer giving a 2.5V signal to AP1, which then means you can adjust the engine speed as required by up to 30 RPM either way.
You need the AP1 input to be enabled for load sharing or synchronising, for stand alone running it is suggested that you disable it with the AP1 Disable input.
Please see attached wiring diagram for this engine.