Mag Drop On 912 UL

by James Mason in 912 / 914 Technical Questions 12 years ago

I have a 912 UL with around 710 hrs. total time. The engine is running well. During mag check prior to take-off, however, the mag check at 4000rpm results in a drop of a bit greater than 200 rpm on each mag and has been this way for years. The engine runs well but it troubles me a bit that this drop is consistant on both top and bottom mag check. Should I be concerned?

Re: Mag Drop On 912 UL

by Roger Lee » 12 years ago

Roger Lee

128 5.28k 4.98k

Hi James,

The good news is it's equal.
It is a little big though. Things like spark plug gap either too big or small will cause this or the carb needle clip set real lean or rich can cause bigger drops. It could be your tach. Does it still sound and run smooth when you do the mag drop?

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Thank you said by: James Mason

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Re: Mag Drop On 912 UL

by Kevin Machniak » 12 years ago

Kevin Machniak

6 167 40

I have experienced high mag drops, when I changed the needle jet clip position.

I have an inflight adjustable propeller , I can change the mag drop numbers with different prop pitches at the 4000 rpm mag check, so possibly prop pitch is cause for the higher numbers you see ? If they are even, I think your good, but I'm just an owner not an expert !

Thank you said by: James Mason

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Re: Mag Drop On 912 UL

by James Mason » 12 years ago

James Mason

11 14 0

Roger: The engine does remain smooth during the mag checks and I am confident that the carb needle clips are set OK since you rebuilt my carbs for me last year and they have been just great. As I said, the mags have always exhibited this drop during run-up for the years (6) that I have owned the aircraft. My bet is that it is just some anomaly in the instrumentation, especially after reading the feedback from yourself and Kevin.

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Mag Drop On 912 UL

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