Slight surging, bad magneto
Posted: Sat Sep 16, 2023 7:42 pm
Posted in case this happens to someone else.
I noticed the airspeed was less than usual for a given power setting. I was also feeling an intermittent acceleration/deceleration of airspeed. It was so subtle I wasn’t sure if I was imagining it. I had to run the engine richer than usual to get the smoothest operation. It took awhile but I final noticed that all four EGT's were going up and down 20 or so degrees. I have linked a YouTube showing the slight EGT and RPM changes. I did an inflight mag check. Fine on the right, backfiring on the left. If I ran it rich enough I could almost smooth out the left. Another thing I found out was a perfectly acceptable mag check on the ground at 2000 RPM. After the inflight mag check I tested on the ground and found anything over 2200 RPM and the left mag would hardly keep the engine running and it was backfiring.
The mags had been IRAN 80 hours prior. The issue was a bad capacitor in the left mag. It’s all fixed now.
[youtube] https://www.youtube.com/watch?v=NOfM5Do1-xc[/youtube]
I noticed the airspeed was less than usual for a given power setting. I was also feeling an intermittent acceleration/deceleration of airspeed. It was so subtle I wasn’t sure if I was imagining it. I had to run the engine richer than usual to get the smoothest operation. It took awhile but I final noticed that all four EGT's were going up and down 20 or so degrees. I have linked a YouTube showing the slight EGT and RPM changes. I did an inflight mag check. Fine on the right, backfiring on the left. If I ran it rich enough I could almost smooth out the left. Another thing I found out was a perfectly acceptable mag check on the ground at 2000 RPM. After the inflight mag check I tested on the ground and found anything over 2200 RPM and the left mag would hardly keep the engine running and it was backfiring.
The mags had been IRAN 80 hours prior. The issue was a bad capacitor in the left mag. It’s all fixed now.
[youtube] https://www.youtube.com/watch?v=NOfM5Do1-xc[/youtube]