RSA Injection Servo.... Impact Tubes

[Andrew Anunson]

My experimental RSA-5AD1 (bendix fuel injection servo) has 4 impact tubes which measure the air pressure at the air inlet to the servo.

There are three different impact tubes that can be installed.... the "Impact Tube $14.91", the "Impact Tube, 1st Over $71.02", or the "Impact Tube, 2nd Over $71.02".

What is the reasoning behind having three different tubes (original, 1st over, 2nd over)? If its for mixture adjustment.... does the 1st over provide enrichment over the standard size?

Thanks!
Andrew Anunson