The coil core has a good earth to the engine block so with the module it's best to earth that to the engine block as well , you can put the module somewhere else as long as it has a good earth back to the motor but the easiest place to install the module is near the underside of the carby ,a pop rivet to hold the module on or you could use a threaded small bolt with a lock nut but then the engine will need to be removed to tighten the nut or you can tap a thread in the cast iron.
