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The difference between Single and Dual Fire

This is our Harley Davidson Hints and Tips series that will help you understand the working of your motorcycle and help with carrying out motorcycle maintenance. So without further ado here is an Electrical Tip.

Electrical Tip

Dual fire
This is the simplest system and the way the earlier, pre-Twin Cam,  engines work.  A single coil is used and both spark plugs fire simultaneously.    The ‘wasted’ spark is sometimes said to be horsepower robbing.

Single Fire
This is the way the stock 2000-Up Twin Cam engines work.   Two separate coils will fire the spark plugs independently and only the spark plug of the cylinder that is on the compression stroke will be fired.  It is said that these engines vibrate less and can improve power.  The effect will become more pronounced with hotter CAM’s and higher RPM.

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