Timing the Secondary Ignition
The AeroVee engine is equiped with a redundant ignition system firing two plugs per cylinder. The primary system is a pair of magnatron units that are energized by the flywheel magnet as it passes by. Because the magnatron units are fixed and the magnet is fixed, this produces a very simple and reliable fixed ignition timing at 28 degrees before top dead center (BTDC)
The secondary ignition system uses a pair of coils and a triggering module. The coils are energized by the aircraft battery and then triggered by a small magnet embedded into the alternator cap.
In my case, the secondary ignition was mis-timed to the magnatrons, and this was causing the engine to run rough and not develop full power. There are several procedures that can be used to time the secondary (timing light, static timing described in the manual, flight testing), and I've tried each one. For me, the best results occurred by using an inductive timing light to get things close, then fine tuning by hand with very small movements and test flights.
When I checked the timing using the timing light, I found that the secondary ignition was pretty far advanced. It's hard to say for sure, but it appeared to be about 20 degrees advanced!
After adjusting the trigger magnet (loosen the socket head screw on the trigger cap, rotate slightly, and then use the light again to check) the engine runs great! The temps are down, vibration is way down, throttle response is better, and the static full throttle rpm went from about 3100 to about 3250. I still can't believe how nicely it runs now that it is timed properly!
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Updated: 3 Jan 07