Hi,
I am no expert in these matters but I have three pieces of information that may help you. You will NOT like them!
First, in tuning the 126 engine the main improvements seem to come from better airflow (so Panda head is good) and larger volume. That is, a 650cc gives more power than 600 cc.
Other changes such as compression ratio, camshaft etc give relatively small improvements, especially bearing in mind the cost of the engineering work involved.
The second observation is that these engines are fairly sensitive to racing or 'sports' cams. I have no experience here, but I listen to what others tell me over many years, and this is what many people with direct experience tell me.
It is generally true that if you change one thing on an engine, then you also have to change some other thing too, to make it work. Having changed the second thing, you then need to change a third thing to make the second thing work. This goes on until at last you have changed the entire engine.
Is this true? If you look at the seriously highly tuned race engines, you find it is true - almost everything in the engine has been replaced with some upgraded or re-engineered part. The truth is that the basic 126 engine is a fairly crude design, and it cannot stand very much extra stress or something will break!
You will find this too with engine changes. If you look at examples where someone has changed the engine to a Subaru or fitted VW cylinders, then you find the clutch will not handle the power, or the gearbox will not handle the power - again, you end up changing the whole engine unit so it is no longer at 126 at all.
As Smallcox has said, you cannot make a high RPM engine with the standard crankshaft as it is too weak.
I said I had three items. So what is no 3?
The third item is your carburettor. I do not know anything about this carburettor, but you may like to see this web site:
http://www.rmcarburetors.net/Tuning%20Tips.htmAccording to this, the jetting of your carburettor is going to be a nightmare to sort out. It is not impossible, but it seems information about the "best" jet or the "correct" jet will be impossible to find. Therefore you will have to work by "trial and error". This means that you will have to obtain different sizes of jets and try them one by one, and hope that you will find one that works. This could be very expensive and take a long time.
So, what to do with your engine?
If you keep using 'extreme' parts in the top end - very high compression, racing cam etc - then it will not make a large change to performance, and it will put stress on the bottom end of the engine which may cause major failure.
You must decide - do you want to change all the bottom parts of the engine as well (new crankshaft etc)? Or do you want to bring back the specification you already have to something less 'racing' ?
It seems to me you have two main immediate problems - one is the camshaft, and the other is the carburettor. I suggest you replace the camshaft to either standard or something closer to standard, and replace the carburettor to a different make (Weber perhaps?) where there is more data available (and more supply of different size jets).
With these changes you will have a less powerful engine, but it may actually run properly! If you go the other way, and keep adding more extreme parts, you will spend much more money, and much more time, and have no certainty that you will ever get the engine to run properly.
I wish you good luck whichever way you choose to go
