What is a Merlin Motor Combo? If you are using the motor from Sincere they will fax a wiring diagram to you. If you can’t figure it out contact me and I will open my motor cover and take a look. If you are using the pulleys you will not need a speed control. Speed controlers are generally used for universal (brush type) motors and vary the voltage. AC induction motors can be controlled with SCR units that vary the duty cycle and frequency but the motors are designed to run at optimum eficiency at the rated frequency. A 60 Hz motor run at 50 Hz will suffer from a loss of power. The way around this in industrial applications is to use larger motors than required so the power loss is not as aparent. Get the wiring diagram first and make sure that your motor is wired correctly or you may fry something.