Fred,

 

Interesting............

 

Are the Mag plugs top, bottom or mixed?  During the break in phase, some engines will actually be, uh, letting more oil into the combustion chamber.  At shut down this tends to accumulate at the bottom of the cylinder where some plugs are located and may have a tendency to more easily become fouled and even more so on the side where one wing is low when parked.

 

Just wonderin'.

 

Grayhawk

 

I have a Lightspeed on one side and a mag on the other side of my IO-550.  I think the key issues with single and dual electronic ignition systems have been well ventilated here, but I wanted to add an anecdote. 

I am completing early flight testing.  After ground runs and brake tests before first flight, touch and goes, a few hours of running very rich as part of break in, and a lot of taxi time, I finally fouled plugs after about six hours.  This was evident during the “mag” check.  Operating on Lightspeed only, there was no problem.  Operating on magneto only, I got a lot of coughing, spluttering, and missing.  I burned the plugs clean with about 2 minutes of 2000 RPM with mixture leaned way out before the engine would run smoothly again with the mag only.  It always ran smoothly with the Lightspeed only.

Conclusion: Lightspeed fires through ugly fouled plugs better than a magneto, just as advertised.  So this might be a benefit in starting if your plugs are somewhat fouled.

Better yet – don’t foul your plugs.

Your mileage may vary.