Originally Posted by Roelof

Ignition timing is done by headshims and glowplug.
Lower compression will give a later ignition
colder plug will give a later ignition.
(by the way: less nitro will give a later ignition as well)
later = more rpm but less power
sooner = more power but les rpm and a hotter engine....
Colder plug with higher compression will keep the timing the same but the higher compression will give more power, the colder plug can give an unstable engine....

Porttiming can be changed mechanical.
Higher ports by grinding the ports out
Higher ports can also be made by adding a modified headshim under the edge of the sleeve
lower ports can only be made by taking off some material from under the edge of the sleeve.
Higher exhaust will give more rpm but lower power, lower exhaust will give more power but les rpm. Widening the exhaust will give more rpm without affecting the power.

Take care with positioning of the sleeve that you change the headshims as well.

Changing crankshaft timing can do a lot to get more power or more rpm, it can only be done by grinding,