Hi Norm
With the surging, I did have a slight surging issue. It required a tachometer to fix - couldn't do it by ear. I didn't know the top speed, so went with 3100. With the engine going, bend the little spring tab to make sure no tension, then get 2900rpm by tensioning the big spring (or 200rpm below top speed), then tension the little spring to get 3100rpm.
But I do think you have a really good point with it having stuff all reciprocal mass. I have just weighed one of the blades off a parts victa vantage 16in. it weighs 225 grams - but the back up lifts are worn flat, so 300g is probably about right
