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Old 01-20-2021, 06:05 PM
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Join Date: Aug 2011
Location: Keller, TX
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Default Help with inflight mag check results

I have an RV-10 with an O-540 and 2 Slick Mags (6351 and 6350). I just had them reconditioned at AIS. During the first flight after reinstalled and timed I did an inflight mag check (23”/2300 rpm). The Left Mag was smooth with EGT rises in all cylinders. The Right Mag ran very rough to the point I went back to both, reduced power to ~18”/2150 rpm and switched back to right mag and saw cy 1 EGT was down over 200 deg.

Cylinder 1 Right Mag fires the bottom plug. I removed the plug and checked the gap, resistance and cleaned it. In the tester with pressure it fired fine. I installed this plug in the top and put the top plug in the bottom so if the problem moved to the Left Mag then it would show there was something wrong with the plug.

On the next flight the Right Mag Ran smoothly with EGT rise across the board as shown in the tables below. However, the Left mag now ran rough but not isolated to #1 cylinder, 3 cylinders had a drop in EGT and 3 had a rise.
The plugs are Tempest UREM40Es with ~100 hours on them and all cleaned and gapped at the condition inspection ~3 hours ago.



The timing was checked and it had not changed. I wanted to make sure the internal timing had not changed due to a failure with the impulse coupling etc.

Now what? I bought a new plug to replace the original suspect plug but doubt that would cause the rough running and affect the other cylinders. It is puzzling that the Left mag ran fine on its own the previous flight and the Right mag had a misfire on #1 cyl and after swapping top and bottom plugs, Right runs fine and left has issues with 3 of the cylinders.

Any Ideas??

Forgot to add that the mag check on the ground is good with about a 70 rpm drop at 1700 rpm with Left and Right mags. The issue is with inflight mag check.

Thanks – TJ
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RV-10 N331JH 3rd owner (First flew in 2005, #15 flying)
Northwest Regional 52F

Last edited by Flying again! : 01-21-2021 at 08:09 AM. Reason: More information added
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