In a perfect engine, each of the pistons will displace EXACTLY the same amount of air.
In a perfect engine, each and every piston ring leaks EXACTLY the same all the others. (zero)
In a perfect engine, each of the head chambers have EXACTLY the same amount of volume.
In a perfect engine, each of the valves open EXACTLY the same height.
In a perfect engine, each of the valves leaks EXACTLY the same amount as all the others. (zero)
In a perfect engine, each of the cam lobes have EXACTLY the same profile.
In a perfect engine, each of the cylinders draw EXACTLY the same amount of air. (See above)
In a perfect engine, each of the carb slides will be open EXACTLY the same amount for all cylinders to fire with the same strength.
A perfect engine is practically impossible. But, even firing pulses from each cylinder can be approximated by feeding each cylinder with a similar charge of fuel/air mix. And, this is acheived when the vacuum present on each intake runner presents the same conditions to identical carburetors.
It's called synching the carburetors. However, the goal is to get all the cylinders to fire evenly.
Now you know why a compression check is good to have done. (cylinder volumetric efficiency check)
Now you know why tappet adjustment and all the tuneup items need be addressed before synching carbs.
Now I'll stop typing,
Cheers,