Failing Mag check

1978 PA32 RT 300 Lycoming I0-540-K1G5D. Just did the mag overhaul less than 30 hours ago and its failing the mag check. Should be no more than 175 RPM drop and no greater than 50 RPM between mags. Testing right mag drops 100RPM left drops 200. Adjusted the points and re timed with same result. Can anyone point me in the right direction to solving this? Starting to think spider, injectors, or engine fuel lines clogging?

Shawn Gehres


  • My guess is that the overhauled mag just failed. Talk to the overhauler and have it redone.

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Piper Owner Society Forum Moderator and Pipers Author.

    Need help? Let me know!

  • The maintenance-induced failure (MIF) theory sounds right on the money to me. Did the shop give you 8130s for both mags, and the data from the test stand run?

    Fuel problem is unlikely, 'cause it should affect both mags equally.

    My favorite debugging technique for this problem is right out of high school auto shop. Using a scope with an inductive current probe, capture the waveform on each of your 12 plug wires. Comparing the waveforms leads to the problem, whether it be a single plug, ignition wire, or the entire mag itself.

    Good luck.


  • Did you get this cured, I had another issue with hard starting on my Warrior and installed a Surefire ignition for the money if it’s available I’d go that way to start and eliminate the 500 hr inspection plus motor runs smother easy hot starts and no worry’s till engine overhaul which is recommended service interval. Good luck with issue.

  • Just a thought check the timing

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