Pmerems

Pmerems

Well Known Member
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Gents,

I am looking for some advice on what to do next.

I was planning on some local flying this morning (nice cool day 51F for a change). During run-up I checked the mags and found the right mag had a 200+ rpm drop with some afterfires (not backfires). I have had this happen only a few times in the past and I went through my normal clearing procedure running up to 2000 rpm and leaning out. This has worked in the past but it didn?t this time. I repeated the procedure several time but it didn?t work. It didn?t occur to me to look at the CHT?s to see if there was one cylinder causing the problem. I should be able to download the data from my Dynon D180 and see.

So I aborted my plans and put the airplane back in the hangar. I am planning to start my conditional inspection this fall (second conditional) so I will be pulling the plugs, cleaning and gapping them, compression and timing check and oil change etc. I was planning to do this over my time off during the Christmas break from work but now I will do this over my extended Thanksgiving break.

So here are the facts:

IO-360 140 TTSN with slick mags. Std Champion spark plugs.
Flying for almost 2 years
Right mag has shown this drop in the past only a few times.
Timing was checked, plugs cleaned, gapped and compression checked 60 hours ago.

Here are my plans to diagnose this:
1. Verify the right mag is actually wired to the right contact on the mag switch. I am 99.9% sure but it is worth a check before pulling the mag.
2. Clean, gap and check the resistance of the spark plugs.
3. Verify timing.
4. Inspect the wiring

The magnetos serial numbers fall within the Slick service bulletin serial numbers but I did speak with Slick tech support at Oshkosh and they said it was very unlikely that I actually would have a problem with the mag if I hadn?t experienced it within the first 50 hours. However it could be the problem.

Any other suggestions?
 
Do another run up!

Do another and check CHT's like you said you should have, before digging into it, might save you some time.
 
EGTs will actually show you more on a bad mag check. EGT will drop off scale with a consistand misfire.
 
Pull the plugs, gap and clean them every 50 hours anyway, and check for resistance (not over 5K).

Start using the red knob the minute you start up. Plenty written here about it. Myself and others have posted many times on the topic.

Unlikely you have a mag issue unless the points are subject to the recent SB.
 
Every so often after my plane sets for more than a week I have a lower plug that fouls with oil. I just do a high power run with the mixture leaned for approx 30 seconds, this usually clears the plug and my mag checks are good.
 
On my trip to ID last year I started having the same problem. Always the right mag. Big drop, after-firing, making a lot of racket! It took longer and longer to clear, so I had to do something.

At Marble Canyon Lodge airport we pulled the cowling and pulled all four right mag plugs, all Champions. They all looked about the same. A well versed RV guy eyed them closely and said that one just didn't look right. He couldn't say exactly what it was, but since I had a spare plug we changed it.

Problem solved! I haven't had an issue since.

I got a good deal on eight new UHRM40E's, so next oil change I am replacing all the plugs and keeping the Champions as spares, as long as they test OK.

So, I'd start by looking at the plugs....
 
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