Andy,
Are you sure you have a Miller stator? It could be either Lucas or Wipac. On the Miller stator, the coils are wired in parallel in banks of 2 and 4. On your stator, the coils are wired in series, effectively in 3 banks of 2. If the internal connections have been changed, you may have some coils giving a positive charge, while others are giving a negative charge, and cancelling out the positive ones!
Regards,
Eddie.
A problem I had was that the coils had become impregnated with finely ground bits of steel (from an engine blow up). Washing the stator and blowing it out with an airline cured the problem (until I started the engine, and the magnetic field generated lined up the particles, and hey prsto - we had a short to earth again). Eventually, I bought some 20 gauge copper wire and rewound the 6 coils. The generator is now wired for 12 volt and easily gives an 8 amp charge.