I changed my pinion to a larger one and went to the flying field for some flights to try it out as I was getting too much bogging on the previous one. I kept the Spirit Gov max rpm settings the same and nothing else was touched.

The first flight was fine but on the second flight I decided to tune the gov settings. I had the Gov response at 6 and holding at 3. I dropped the response to 5 and holding to 1 so I could begin tuning per the Spirit manual.

Spooled up and my top 3100 headspeed was no longer being achieved. was maxing out around 2750. Changing between all 3 Idle Up settings had no effect on the headspeed. Each IU was the same ~2750rpm. Confused, I began checking to see if my pack had blown a cell, nope. So I decided to return the settings to 6 & 3 as they once were. Turns out that dropping the Holding from 3 to 1 was the reason the governing stopped working as expected. Going back to 3 returned the gov to the 3100 I was expecting. It was around 0ºC today, but am really confused by this behaviour. Any explanation for it?

When changing pinion you have to change Gear Ratio respectively.
Otherwise the headspeed will be calculated incorrectly. Then it will also hold at a wrong RPM.

_________________
Spirit System developer

Doh! Yep, definitely forgot to change that.

Wonder why it provided me with expected varying rpm's on each IU with the holding set at 3, but then the same exact rpm on each IU once I dropped the holding to value to 1 though. Would have expected different values still (but incorrect) without changing the gear ratio.

Gear ratio changed which fully resolved the issues I was seeing.