912ULS Ignition Issue

Hello,

We have a 912ULS engine, 200 hours since new that produces vibration that feels like one cylinder does not fire when on the left ignition switch.  The RPM gauge is within the allowable RPM drop; close to 200 but a rough running condition persists.  Visually,  I can see the vibrate.

We switched the vertical connectors on the ignition modules and the problem follows the module - meaning the right position now produces the problem.  

The problem only appears at or above 4000 RPM at 3500 no issue with the ignition check.

Any thoughts/other checks?

Thanks

Don