After spending the last 8 years installing and dyno tuning programmable ignitions I have yet to see more than 0.2hp difference in any engine by changing the ignition advance(by as much as +/- 7deg) , off the pipe. All adding advance will do is help the engine get on the pipe faster.
With that said it's of no use moving the stator around unless you know how much advance/retard your ignition currently has. You will more than likely find that the standard settings (measured with a dial gauge and strobed against the flywheel) provides the best "all round" performance and usualy 1 width of the stator mark either side of the reference mark is for fast and slow tracks. Modern DC/DC ignitions have far more voltage delivered to the plug, regardless of rpm, more accurate timing and smaller and more compact flywheels/stators. Along with 3D mapping etc etc
I agree. Modern ignitions with much smaller rotors and better pick ups/stators are so much easier to live with. And they give a much fatter spark from near zero to whoa.
Changing ignition timing won't get more power, but you can change the way the power comes on, both in 2st and 4st engines. As you say, advance makes everything happen quicker. Myself, I like having a little retard on my 2st bikes as it helps to give a bit of bottom to mid range power that doesn't come on in one big explosive burst. It actually helps to make the motor more tractable. After years of being told to advance the ignition, Gary Jones put me in the right direction.....
Personally, I'd try going bigger on the pilot jet. Put a big enough jet in there to make the bike "burble" at 1/8th throttle (just opening), then remove it and go 2 sizes smaller. This should put you in the ball park. GJ also put me onto this.
And yes, expansion chambers make a huge difference to how a 2st engine behaves. My memory of my old PE400 was that of a very tractable motor with heaps of low to mid torque. It had the stock chamber but I put an alloy silencer on it for no other reason than to save the original from battle scars.