We gone do some calculation to understand the powerboard,

To get a big/strong spark, we need Joules.....a lott of Joules, mega Joules.
For a good spark and a high rpm we need about 90 mJ. (45 mJ for ~8000 rpm)
This Joules we get from the capacitor and the high voltage coil on the powerboard.
If we have 300 Volt from the coil and the capacitor is 1 uf, we have (0,5*C*(U*U)) = (0,5*1*(300*300)) = 45 mJ
With this calculation you can see we don't have enough Joules.
Wat can we do about this.....
Increas the capacitor, but you get a longer load time....not good !
Increas the voltage, easy to do......more windings.
If we have 600 Volt from the coil, we get (0,5*1*(600*600)) = 180 mJ, we need only 90 mJ !
Now we can decreas the capacitor to 0.5 mF, this will also decreas the laodtime from the capacitor to 1/2 of the normal loadtime.
If the laodtime from the capacitor will be shorter, the rpm will be increas.
We need also some current with this voltage.
A easy way to do this is to wind prim two windings (to gether) on the coil (2x 20 windings of 0.5mm).
The sec-winding must be increas to ~1200 of 0.1mm to get ~600 Volt.
BTW, don't forget to make the resistor of the ocsilator smaller ~1/2 of the normal value for a higher rpm.