yes the key is much bigger than the original,
i would suspect but i dont know how big the old one was
i was thinking about flywheel ballance, and you saying that steel weighs 3 times more than alloy makes a bit more sense, but i would not have thought a gram or two that close to the crank would make much of a diference, i might try adding some weight to the opposite side or removeing a little from the side the pin is on...... a small hole from a drill maybe going off your calculations of 3:1 and placement on flywheel or maybe drop it off to a shop for a ballance job,, but maybe if i add some weight to begin with and see if it operates any difrently might give more of a clue.. its hard because i dont know the history of the trimmer or how it was stuffed,, ill i know is someone gave it the toss in the rubbish bin
id love to get a new flywheel but in australia these parts are very hard to come by
