get a baseline and go from there. start out with a slightly larger two needle carb (both Zama and Walbro make them, both have the same bolt spacing but the pulse hole is sometims in different places), also gut the stock muffler and give it a couple 1/2" ID outlet tubes. These two changes will imcrease the power from the factory specs, they had it choked down with an air filter and a small carb, along with a tiny exhaust outlet

if that's still not enough for you, take some plumbers solder and put it through the spark plug hole and smash it with the piston at the cylinder wall in the combustion chamber, measure that distance, that will give you how far the cylinder can go down to increase compression, a lot of times it's just enough to fix up by removing the gasket and sealing it with some RTV, from there, print yourself out a degree wheel and check the duration of the intake and exhaust ports, I hear a maximum for the exhaust should be 150*, I don't remember intake off hand.

those are the main power adders unless you jump to a tuned pipe