Though not necessarily specific to an aircraft engine, I've run across some information concerning an after-market ignition system for Zenoah engines that has me a bit baffled. It may very well just be that my comprehension of the subject is more limited than I already thought. Anyway, the ignition is from MSD and specifically designed for the small Zenoah 2-strokes found on go-ped brand 2 wheel scooters. In stock form, the engine has a fixed magneto ignition. The MSD is a CDI type ignition with adjustable retard from .5 to 1 degrees per every 1000 rpm.
The installation manual for the MSD ignition says to set the static timing at about 27 degrees BTDC. Then adjust the retard rate for best performance. This means the ignition will retard the timing as engine rpm increases. I was thought it was desirable to advance the engine timing for the upper rpm for best performance and have less timing for starting and low rpm operations?
The reason I am inquiring concerning this subject is because I am interested in adapting the small MSD ignition for installation on another brand of small 2-stroke and not a Zenoah as it is designed. The engine is not for an aircraft.
Here is a link to the manual for the MSD ignition.
I don't understand why it would be desirable to retard the timing at higher rpm. This is contrary to what I though was appropriate.
Thanks for any input.
John