I have had this exact same problem and have jsut had my ignition swapped under warranty. The firs tsign of tyhe fault was a severe drop in power of the engine, by 500rpm+. Then it would only start on one cylinder, was fine in the air, but rpm would hunt up and down. Finally one cylinder died altogether. I have been informed that it is the light and delicate coils used to generate the HT for ignition. They are possibly sensitive to battery overvoltage fresh of the charge, or by being left in a charged state and then discharged in an abnormal fashion (ie accidental short while diagnosing faults etc). I have also been told not to use a 5-cell pack with the ignition system as of course this is producing 7+v fresh off the charge which is way over the rated voltage. So im now using a 3000 4.8v pack and it seems fine. Other option is to use LiPo or 5-cells with regulator, one wonders why DA dont install one themselves?