Is modifying the vacuum piston and spring of a CV carburetor a good idea?

More about carburetors here:    • Constant-velocity carburetors  

Constant-velocity carburetors were designed to remedy certain deficiencies of mechanical-slide carbs. Accordingly, modifications of some components of a CV carb may, ultimately, hurt drivability and performance. If the butterfly valve is suddenly opened when riding at part throttle, both the velocity and the vacuum in the venturi decrease momentarily. To compensate, the vacuum piston lags behind the butterfly valve (perhaps even drops?) for an instant. The job of the vacuum piston is to keep the velocity of air through the venturi as constant as possible. Modifying the spring and the vacuum piston CAN be beneficial for racing applications if done properly, but for
every-day use, it's best to leave these components alone.

The dimensions of the vacuum port, provided in the video, are for a Harley-Davidson's Keihin CV-40 pumper carb.

In the video, I neglected to mention the importance of the correct fuel level in the float bowls (best float height for full-throttle power at low rpm) for purposes of correctly tuning the carbs. Watch this video series for more info:    • Carburetor fuel level and its signifi...  
























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