Jim, this info is for RC and Yoshi mags.
The advantage of magneto systems over conventional ignition systems is superior spark producing capability at high engine speeds without using the battery as the power source.
Another important advantage is that the magneto fires only one plug at a time.
Stock ignition will not always work well with a modified engine. As anyone knows, Honda fires 2 plugs simultaneously. One fires just before the intake stroke, one on the power stroke. This is fine with a stock cam.
However with a hot cam, the intake valve is open when the coil fires. This can partially fire the incoming mixture and reduce the efficiency of the engine. Even a good CDI does not solve this problem. Racing engines are not required to have a battery, so the weight saved by removing it gives the magneto a decided advantage. On a street bike which needs a battery for lighting and an electric starter, a magneto may not improve performance over the stock ignition system enough to warrant the expence and effort.
Installation/Timing.
1. Remove the points cover.
2. Remove the valve cover caps on the No 1 cylinder.
3. Turn engine to top dead center of No 1 cylinder with both valves closed.
4. Place transmission in 5th gear to keep engine from turning.
5. Remove point plate assembly, advance unit and stud.
6. Remove magneto outer drive cover and drive stud.
7. Remove O-ring from Honda point stud and install on magneto stud.
8. Install magneto stud in crankshaft and tighten with allen wrench inserted in predrilled hole.
9. Turn magneto so that line on large pulley lines up with line on magneto case. The magneto is now firing on the No 1 cylinder.
10. Recheck engine to ensure that TDC of No 1 cylinder is still retained. The pin hole in the crankshaft should be in line with Honda timing mark.
11. Install magneto on engine, ensuring that pin in magneto drive aligns with hole in crank.
12. Install 5 screws and tighten securely.
13. Install long center bolt and tighten.
14. The No 1 plug wire is marked and is located at 11 o'clock position as viewed from the left side of the engine.
15. Firing order is 1-2-4-3 counterclockwise rotation.
16. Timing is pre-set at 35 degrees. If a change is desired, loosen the center 7/16 in bolt. Loosen small allen set screws in drive pulley and rotate to desired timing position using a degree wheel to determine crankshaft position.
17. Retighten allen set screws (do not overtighten). This only holds pulley in place while timing magneto. Retighten large certer bolt.
18. Points should be set at 0.014-0.016 in. (0.36-0.40mm); plugs at 0.020 in. (0.51mm).
Hope this is of some use to you as it has taken me a full hour to type.
Good luck, best regards Sam.
