Broadly speaking, more advance gives more bottom end, but also more pinging - so it sounds like you're stuck between a rock and a hard place.
However, given that the 125F is a peaky bitch of a thing to start with, maybe you're simply too advanced.
Is the jetting/plug/etc right?
Timing should be 1.2mm BTDC - and don't trust the marks on the stator coil and rotor, as they rarely actually line up when the ignition is firing.
What I have done, is find 1.2mm BTDC, and mark the stator and rotor at that point. Then use a timing light to set the ignition to that mark (at a low idle! If you rev the bike, you should be able to see the timing become more advanced).
Oh, and apparently an E barrel helps make the bike rideable. You also need an E pipe to match the barrel.
