I have the EXACT same problem on a motor i just put together, this motor also has a ricky stator... before I look very far, i am going to replace it with a stock stator. The motor idols perfect and sounds great, you can ride it around perfect at low rpm's right up to were the powerband hits and the revs shoot up... it's very consistant on were it breaks up. let me know if you find out anything, and i will do the same.