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Iron Sportster ignition systems
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Left coils are factory 1965 and later 12V coils. They also make a 6V coil in this shape. Early coils were large vertical units. Top right is a Crane aftermarket the bottom right is a Dyna aftermarket, the orange is a mystey aftermarket. RH top and bottom are 12V factory, middle bottom is 12V 1985 and later. 31609-52 are 6V coils used 1952 ~ 1958. 31609-52A are 6V improved 1958-64. 31609-52B are 6V retrofit with new shape. 31609-65 are 12V like LH above. 31609-65A are improved retrofit ~ 1978. 31609-80 like LH above, 1980-1984. 31614-83 like middle bottom, 1985-1999. There are aftermarket setups where you use two coils, one for each spark plug. This needs a "single fire" module. Or you can use the above dual-fire coils in dual-plug bikes, with one coil running the two spark plugs in each cylinder. Many aftermarket coils brag about having lower resistance, 2 ohms or less. A factory 12V coil is 5.8 ohms. It works fine in dual-fire mode for any RPM a stock Sportster can achieve. Lower resistance coils are harder on the battery and will drag down the generator voltage at idle. For simplicity, a stock coil and mechanical advance works, but check those advance weights. For electric start only, a 1983 factory setup (or aftermarket) with VOES switch is best. The factory module may not work with kickstart bikes. |
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