The internal combustion engine is designed to do one thing; burn fuel and air and convert it into reciprocating energy.
The one thing that provides this critical element to your engine is the carburetor. You can modify your engine all you want, but if you do not provide the correct ratio and properly atomized mixture of fuel and air, your engine (and all that modification) simply cannot perform at its optimum level of efficiency and provide maximum power.
Here is an example of how critical the carburetor is: whenever a vehicle manufacturer such as General Motors designs a change to an engine or drive train, they also design and calibrate a carburetor specific to that vehicle. Even a change as small as 10 or 20 horsepower, or a manual versus automatic transmission receives a different, custom tuned carburetor. If profit driven, cost conscious manufacturers were willing to spend the additional time, resources and finances to engineer a carburetor specific to applications that are seemingly as similar as these. This clearly emphasizes the importance of a properly engineered, custom calibrated carburetor.