Sure. The amount of power you get from any engine is a function of how much oxygen you can get into the combustion chamber. It is the limiting factor because you are restricted by the available oxygen in the atmosphere (unless you artificially add oxygen). Generally, it is a straightforward task to supply the corresponding amount of fuel, so considering how to get more "air" in somewhat simplifies how to do it. There are several ways, and the principles usually overlap. The simplest to understand (not necessarily the easiest to physically implement) is to make the mechanical pumping action better. In a 4 cycle engine this means things like improving the flow of gasses in the intake and exhaust, fooling around with the cam to hold the valves open longer, or making the piston larger to make a bigger "pump". This concept will only take you so far, because the pumping action of a piston engine is not continuous, but in fact massively intermittent. On the human scale, it seems like air is continuously sucked into the engine, but this is only so because the intake "pulses" occur so rapidly. This intermittentcy is another potential source of adding air. As valves open and close, they very abruptly start and stop very high velocity gas (air/fuel mixture on the intake side, exhaust gases on the exhaust), and when they do, a shock wave is created that travels along the pipe in which the gases are traveling. This can have a very positive or negative effect, either pulling gasses along or pushing back against the flow. These shock waves travel at the speed of sound, and are unaffected by the speed of the gases, but very much affected by their density and temperature. When a wave reaches and exits the end of a pipe, an inverse wave is created and travels through the gases back down the same pipe. These waves pass through each other, also without ill effect, and if you can get one to arrive at just the right time, say a positive wave arriving just as the intake valve closes, this wave will "push" intake mixture through the closing valve. In a high performance application, you probably designed your cam shaft to hold the intake valve open longer than mechanically needed, so that inhaled intake mixture would actually be pushed out the valve into the intake tract as the piston ascends on its compression stroke. If you get that shock wave to arrive at just the right time, it can be counted on to stuff that escaping intake charge back into the combustion chamber along with some extra it is carrying along, effectively supercharging the pressure of the combustion chamber (at the bottom of the stroke) to above atmospheric. In other words, adding more oxygen than would be possible with just a simple mechanical pump. This effect works in the exhaust as well, where you would like negative waves arriving when the exhaust valve opens to suck the spent charge out of the chamber, and a positive to arrive before the valve closes to stuff any new intake charge rushing past the valve back into the combustion chamber - sort of a reverse supercharging. This is principally why a good set of "headers" adds power, simply reducing the exhausts restriction does not help much unless the OEM exhaust is really bad. Otherwise, simply removing the exhaust altogether would work. Another thing to consider is air temperature and density (and humidity). Cool, dry air contains more oxygen, so sourcing the engine air from a cool location is a good idea.
Obviously a lot of this is pretty complicated to both figure out and actually implement, which is why re-engineering an engine for more power and also getting it to run well under all conditions is challenging. Extremely challenging with new engines, as very smart people have likely found a better balance of functionality vs. max output that most of us can. With an old engine, you still have a pretty good shot though. Start with the easy and basic stuff first, and do one thing at a time so you can back track if things don't work out. Typically, one would start with the intake and exhaust. This is practical on an old engine, as sound volume is very important on a stock bike, and a compromise not allowable when designed. If you are ok with a lot more noise, often there is power to be had in exchange. After that most folks start looking at redesigning the camshaft(s), intake and exhaust port profiles and compression ratios and head design. If you can, it is a LOT easier to simply make the engine bigger by increasing the displacement. You suck in more air with more oxygen, and generally keep all the complicated stuff the same. At some point, you can get all these modifications to work well, and the amount of air the engine can suck in will exceed what will flow through the carburetor easily. Make the carb bigger, and the problem goes away - but there are a few things to remember. The first is that carburetors need very high air speed through them to atomize fuel sufficiently. This is easy in a small carb (for the engine) as the big air volume through the small carb bore results in high air speed. As the carb gets bigger, the air speed goes down and the atomization becomes poor. This is important for two reasons. Actually one, but it is at least two parts. Your engine can NOT use liquid fuel. The fuel must be changed into a gas before it will chemically react with the oxygen. So you need the tiniest drops possible, or they can not be used. Because there is a crazy short time span in which the drops can evaporate, the drop size is super important. You need really good atomization all the time which generally means a smaller bore than would be optimal for max power. So you get the tiny drops, it can all evaporate, and combine with all the available oxygen. This evaporation is a key element in the process, not just because it is required to burn, but because it is critical for cooling (the part 2!). When a liquid turns into a gas, it changes phase. Making this phase change requires substantial energy which is provided as heat from the engine. Without this physics phenomenon, our engines would not be possible - no amount of external water cooling would be enough. In fact, this is the reason that it is virtually impossible to run engines as lean as the chemical reaction ratio would suggest: The extra fuel is needed for cooling, and the better atomization, the more phase change, and the less fuel wasted.