How to check and adjust the vacuum-operated electric switch (VOES) -- Harley-Davidson Evo

The VOES is used to select between the two available spark-control curves of the ignition control module (ICM) on almost all of H-D's evolution motorcycles (some used a MAP or Manifold Absolute Pressure sensor). For lighter motorcycles, such as XL, Dyna, and FXR models, the vacuum set point of the VOES is between 3.5 and 4.5 inches of mercury vacuum (in other words, the VOES switches ON [CLOSES] and grounds the ICM to ADVANCE the timing when vacuum in the intake manifold is at or above the set point). The VOES of the heavier bikes has a higher set point: 5 to 6 inches of mercury vacuum for late FLTs and around 7 inches of mercury vacuum for the early ones. When the engine is under load, and manifold vacuum drops to a point below the vacuum set point of the VOES, the VOES opens and timing is RETARDED (spark-control curve with less advance is now used) to prevent detonation. Of course, aside from engine load, which is sensed by the VOES, ignition timing also depends on engine RPM -- higher engine speeds require more spark advance than is needed at lower RPM or during start-up. The effect of the VOES on ignition timing is superimposed over the RPM-based ignition-advance requirements. The vacuum "advance" feature on older cars works in a similar manner to the VOES -- it is really a vacuum "retard" of ignition timing under high-load conditions.
Harley Davidson, HD, H-D, Dyna, FXR, FXRP, FXRS, FXRD, FXRT, Softail, FXST, FLH, FLT, Wide Glide, Low Rider, Super glide, Sportster, XL, Springer

[@susieroberts8175]

Very clear - thank you so much! 😊

[@Zerk_Ziegler]

You are very welcome. Please see video description for additional details.

[@vectorelectric8489]

Thank you very much.

[@Zerk_Ziegler]

👍

[@RevoGamingON]

Will this cause no spark if it is bad?

[@Zerk_Ziegler]

When the VOES fails, it does so in the open position, which means that ignition timing will always be retarded. But the bike will still run. However, throttle response will suffer somewhat.