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Re: Carburetion.

To: Steve@olsonarchitect.com, datsun-roadsters@autox.team.net
Subject: Re: Carburetion.
From: Keith0alan@aol.com
Date: Tue, 6 Jun 2006 21:25:47 EDT
The SU is also referred to as a "constant velocity" carb. Not exactly  
correct but the velocity and "signal" (vacuum at the jet) are fairly constant.  
The 
piston acts like the mass air flow sensor and the needle is like the fuel  map 
chip in a modern fuel injection system. Because if it's ability to measure  
air flow the SU is less sensitive to atmospheric changes such as altitude. This 
 renders the question of "what is a good high altitude needle?" fairly moot. 
 
When I started flow bench testing SUs I saw something interesting. With the  
throttle wide open, slowly bring up the manifold vacuum. Nothing much happens  
till a certain vacuum level is reached. At that point the slide goes from 
fully  closed to fully open almost at once. It is trying to maintain that 
constant  vacuum level and pretty much switching from closed to open when that 
threshold  is reached. 
 
keith williams
 
 
In a message dated 6/6/2006 3:56:01 P.M. Pacific Standard Time,  
Steve@olsonarchitect.com writes:

Does  this mean that the air velocity is maintained constant by the rising
piston  in the SU carb?




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