double spark problem?

[mainstand]

For solid reliable mileage you could ask for no more Pete.

[Scooter Paul]

MB have just announced that they will be selling, in the new year, a gizmo to 'clean up' this issue. From the photo it looks like a plug and play easy solution. Maybe an adult may come along and explain how it might work. Also claims to remove Rev limiters from CDI's.

Paul

[Steve J]

The problem with the AF flywheels would often show up only at high revs. My theory is that the non-magnetic brass rivet/plug in the middle of the AF flywheel pole piece means that the magnetic field is not uniform across the face of the pole pieces. At low revs, the pickup coil will trigger the CDI correctly, and will also pick up smaller voltages from these 'non-uniformities' (for want of a better description) in the middle of the pole pieces. No problem, as the voltage will be too low to trigger the CDI. As engine speed increases, the correct trigger pulse will increase in amplitude, as will the rogue pulses. At some point, the peak voltage from these unwanted pulses will be sufficient to trigger the CDI, and all hell breaks loose.
When I had the original AF flywheel on (about 5 years ago), a strobe light would pick up the normal firing pulse, plus others at regular intervals around the flywheel, corresponding to the positions where the centres of the pole pieces passed the trigger coil. I solved the problem by drilling out the brass rivets, and replacing them with six countersunk M6 steel screws from the outside of the flywheel - just like on the SIL flywheels. I trimmed the inner ends of these screws where they projected through the pole pieces, and used Loctite on the threads. After that, there was just one trigger pulse per revolution - job done. If anyone wants to do the same, I'd recommend that the drilling, tapping & countersinking operations are done just one pole piece at a time, and that the pole piece is very firmly clamped in place throughout the operation - otherwise, it will move (don't ask me how I know). Another thing - it's a messy job, and lots of magnetic swarf seems to get trapped in the drill/tap used, so clean them out regularly. I'd also budget for more than one set of drills/taps, as they seem to go blunt very quickly.
If a bolt-on solution to this is available, it sounds like some sort of simple electronic circuit which will only allow the highest amplitude pulses to pass from the trigger to the CDI, and will block the lower amplitude rogue pulses. If it works, fine, but the root cause of the problem is in the manufacture of the flywheel - a manufacturer putting the things together without having a basic understanding of electromagnetic theory, and using the wrong materials. If the same sort of problem is occurring with the BGM flywheel, I'd be taking a close look at the way the flywheel is constructed, and the materials used.