20% increase in BHP and torque is quite a claim for the work that was done, William. It must have run like a dog before? 
Actually not so, it ran within its design parameters, no better or worse than most modern mass produced machines. However, those parameters, this retired test and development engineer found unacceptable.
To get back to Descoladas original post
"Is there any such thing as performance tuning on a wee (AK9). Can the engine be tweaked to provide more power - without workshop performance testing tools/diagnostic how would you know that your wee is performing at its optimal efficiency?" First some basic notes on engine/performance tuning; there are three areas that affect power output:
1. Internal modifications such as bore size, cam profile and valve size, etc.
2. External modifications such as exhaust size, end can design and inlet filtration methods, etc.
3. And this is the critical bit, the harmonization of all the various parts to deliver the optimum power and torque at any given revolution.
Back in the days of non ECU controlled power delivery there existed many talented men capable of such tasks who could extract that little extra that gave top racers that crucial edge. Men such as Tom Arter, Joe Craig, Francis Beart, etc became legendary names in engine tuning. These men could determine the optimum fuelling and ignition settings allied to spark plug readings to deliver the ultimate performance tuning.
With the advent of the ECU controlled motorcycle power units a new generation of tuner has emerged, however the principles remain the same I.e. number 3 of my basic notes.
So back to the principles of performance tuning; initially all original manufacturers specifications should be established (I.e. standard exhaust, spark plugs, air filter, valve clearances, etc.) then onto the dyno to check BHP and torque output at any given engine revolution. The modern tuner can then re-set the parameters of power delivery to suit a given riders requirements within the tolerances of average climate conditions and altitude variations. In many cases the average power increase on a variety of different make machines has been found to be approximately 20%. As a note, back in the days of carburettor equipped machines I often found that fitting slightly larger carbs to a machine even without gas flowing cylinder heads would when dyno tested increase power output by a similar 20%.
So to sum up, on modern ECU controlled machines remapping will give the maximum performance gain for the given financial outlay and that can be proven by the dyno read-out, any after-market bolt-on I.e. exhaust end can, air filter, etc, effectiveness can only be proven on a dyno test.
Not trying to be clever with this post but merely trying to answer the original post clearly and concisely.
