JEH Ignition
Sounds like you have a classic case of not enough dwell, about the only "downfall" you can get into with this system. You will find you will need to install more than one magnet. I have gone over this thoroughly with Jerry. With the one magnet, you do not have the coil "turned on" long enough for it to charge properly at higher rpm's. Here is a picture of how to easily figure it out.
Good luck,
AV8TOR