ROTAX Tach readings erratic at RPM > ~4,500

BrentC48

I love flying!
Joined
Jan 5, 2014
Messages
16
Location
Hackettstown
I'm preparing for first flight and was adjusting prop pitch on an RV-12 / Rotax 912 ULS engine.  At wide open throttle (>4,500 RPM) I am seeing highly unusual RPM readings.  At low/warm up RPM up to above 4,000 the tach appears to be steady.  But as I approached 4,500 or so, the tach readings are all over the place.  Second by second, the reported RPM jumps around to redline, back to mid 4,000s or so.  The engine didn't sound like it was changing true RPM rates at all, so it appears to be an instrumentation issue.  Note, in previous ground run-ups when approaching WOT I've not seen this before.  I've not yet downloaded the data files from Skyview, but those are available should they be useful.   

I've read in the last day of similar reports with the Dynon tach/Skyview on another website, and there were some comments about the need for the installation of a "resistor" in the lead that feeds into Skyview from the tach?

Would appreciate some direction as to whether this makes sense and what exactly is the correct parts/method to install such a fix.
 
Top