All the features of the famous Dyna "S", plus the special feature of firing the front and rear cylinders independent of each other, allowing a much more accurate timing of each cylinder. The stock ignition system fires both cylinders at the same time, which works fine for the front cylinder but the rear receives the "wasted" spark when the cylinder has started its intake stroke; this can result in harder starting, increased engine vibration, backfire and raw fuel being spit back into the carb, all creating a power loss. Dyno and top-speed testing have shown a dramatic improvement in power in all areas; bikes with hotter cams show the greatest improvement. If you truly want to get the most out of your stock, slightly modified or all-out customized Harley-Davidson, you need a Dyna "S" single-fire ignition system. Not recommended for use with OEM coils.. On 84-up Harley-Davidsons, an advance weight mechanism is required.. This unit must be used with special Dyna coils. Tach adapter is required when using an electric tach.. Not for fuel-injected models. Made in the U.S.A..
