im guessing timbone came the closest...there is, imho, a major lack of engine support here, causing the issue.
that lil dangly bit, that creates the front motor mount...where does its other end join up? nowhere. left dangling in the breeze. hang a ruler off the edge of the table and give it a wack...TWANG. exactly whats happening here...the things just going to vibrate until the other end is secured. another analogy? your motor is sitting on the end of the springboard, contemplating a triple backflip and half turn into the swimming pool... its called a "clamped cantilever" and theres whole books available that are dedicated to describing the way they vibrate...
you tried the wizz bang, over hyped CDI modification...did it do anything? no. or you wouldnt be here, posting. so why would balancing or lightening anything make any difference? sure, throw money at it. still wont fix that glaring design fault inherent in the frame.
you cant balance a single cylinder. can reduce the severity to some degree, but what you remove from the up and down movement of the piston, will just appear as a rotating mass on the crankshaft(that acts in all directions as the crank revolves...so its up, down, forwards, backwards, and all points in between). so you lighten the shaft to compensate, and now the pistons back to its up and down movement...so you lighten that, ad nauseum... at some point youre going to run out of engine!
save your money. get the engine mount attached at BOTH ENDS. how? thats your concern
"but thats how they sell them"... i assure you, everyone else that has a frame with an engine mount like that is ALSO getting buzzed around, titanium gudgeon pins not withstanding.
all pistons are the same...give or take. drilling holes just reduces strength. really good idea when they accelerate and decelerate a few hundred times a second
oh, it may just be my "fragile ego" but according to my tach..im happily hitting 8000 rpm and still using my rearview... and this current engines so far, "stock"... there are definite sweet spots in the rpm range, i wont argue with that. its the nature of ANY rotating part, to have "critical speeds" where harmonics and resonance can increase to the point of failure. certain heavy machinery needs to be accelerated very carefully past such speeds... watch something as "round" as a bench grinder slow down
theres always a point where it tries to shake the whole shed to pieces! THAT is the critical speed, and running it at that RPM will cause it to explode!