The rpm is sensed by the g3x from the digital tach signal output on the pmag. you can hear that the rpm is fluctuating and garmin pilot shows the fluctuations. I will probably change the restrictor or add a smaller one to try and damp out the fluctuations.
Could a resonance be caused in the vacuum tube to the mags causing the timing to go out at both 1150 and 2300rpm?
Are pmags more sensitive to vacuum?