A lot of people think its to do with the bits of brass that hold the magnets in.
I haven't ever had this problem but i have had clearance issues as they are so close to the stator and i had one on a piston port Mugello 225 and no matter what you done to the jetting it ticked over like a bag of s**t!
I put a 2kg flywheel on and it ticked over lovely. I would consider an af flywheel on a reed motor but as i have said earlier, in my opinion on a piston port motor they are too light.
They look very nice though!
