Carburetor balancing on multi-carb, multi-cylinder engines is very important. Each carb must supply the same amount of mixture (fuel and air mixed) for the engine to run smoothly, develop good power, and maintain fuel economy.
The most accurate method of balancing these types of carburation systems is by using vacuum gauges (see note regarding rebuilt carbs). When attached to the inlet systems, the vacuum gauges measure the amount of vacuum drawn on each gauge as the engine is running. The effectiveness of this system is evident as the carbs are adjusted: small adjustments can be seen on the gauges as the carbs are adjusted.
Capable of Greater RPM
For example, as the carbs are brought back into adjustment (assuming they were out in the first place) the engine idle rpm (revs per minute) will increase. Effectively, this indicates that for a given throttle position, the engine was capable of pulling greater rpm.