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Speedy Squirrel Speedy Squirrel is offline
Rocket Scientist
Join Date: Jun 2008
Location: Detroit
Posts: 906
First, it is a vacumn limiter, not a decel valve. It is not active during open pedal, unless it is broken, or the idle adjustment screw is opened too far, so it should have no impact on open pedal operation.

It has a simple job. There is a slight lag between when the throttle closes, and when the airflow meter reacts to the reduced airflow. Due to this delay a small amount of "extra" fuel is injected when the throttle is quickly closed. The vacumn limiter "burps" a little extra air into the intake to combust the fuel in the chamber, rather than have it go off in the exhaust and make the farting sound.

Normally the extra fuel is too small to produce enough positive torque to notice. However, many CIS systems are set quite rich, in which case some throttle lag is noticable.
Old 04-16-2014, 08:39 AM
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