How do you eliminate engine sputter on a 2005 Harley Road King?

A "sputtering" engine can be caused by several possible problems, such as: Weak spark (caused by fouled plugs, a bad spark plug, a bad ignition coil, a bad ignition module, poor timing, or even a loose ground connection from the battery to the frame.) Bad Gasoline (can be caused by old gas sitting for several weeks). Poor injection function. Air intake limited (air filter dirty or obstructed) To diagnose this yourself would require a copy of the appropriate Service Manual for your year of bike, a good electrical multimeter, and time. To allow the dealer to do this would only require many hundreds of dollars.