A control circuit for a coiled tubing injector includes a circuit controller (14). One or more counterbalance vales (3) may be responsive to the circuit controller to prevent the tubing string from descending into the wellbore during rate of penetration movement. In one embodiment, a control valve (4) allows fluid to flow through a bypass line around the counterbalance valves when drilling in a weight-on-bit mode. Other hydraulic control circuits allow for the release of fluid pressure to control the injector hydraulic motor. In yet another embodiment, the control circuit regulates power to an electric motor of the injector.