How many times have you heard of people working for days or even months trying to track town an intermittent stumble or hard starting problem on their air head BMWs, only to find that a defective coil was at the heart of the problem? As our airheads age the epoxy that separates primary and secondary windings becomes brittle, and if it cracks, it may not generate sufficient secondary voltage to fire the spark plug. The problem seems common enough to warrant proactive steps to avoid it. Rick Jones at Motorrad Elektrik recommends the Dyna coil, and I found the installation very straight forward and the results indistinguishable from the original. Except, hopefully, in long term reliability. The BMW coil lives up under the fuel tank just behind the head tube, and the first job in making the swap is to remove it. Pull the two primary leads off the spade terminals, and remove the two socket head cap screws that hold it to the frame. Pull the plug wires off the coil if you're going to reuse them, otherwise pull the plug leads off the spark plugs.