it's a long shot, but are the plug wires routed correctly? As you know,
on that engine, one mag runs all the tops, and the other all the
bottoms. Maybe someone installed them in the more conventional,
staggared arrangement? Just SWAG...

Happy Flying!
Scott Skylane
N 92054

I should have mentioned that I did confirm this. I should note that everything
"wire wise" is the same. I replaced only the right mag but not the wires. That
bad mag, of course, would hardly run correctly for a minute at a time.

Jim