cis mixture

[Alan Cottrill]

I just want to make sure I understand this.

The screw between the fuel distributor and intake boot controls the "idle mixture".

when the engine comes off idle that adjustment means nothing and the only thing that controls the mixture is control pressure.

do I have this right?

[Hladun]

No, you are changing the air plate versus fuel control valve height relationship. However the effect may not be proportional.

[beepbeep]

Originally posted by Alan Cottrill
I just want to make sure I understand this.

The screw between the fuel distributor and intake boot controls the "idle mixture".

when the engine comes off idle that adjustment means nothing and the only thing that controls the mixture is control pressure.

do I have this right?

I tought so beacuse i've seen that sort of adjustment on CIS-diagrams i've studied but have been tought otherwise when it comes to Porsche CIS...

[Superman]

Porsche CIS has no special magic compared to other CIS. Fuel pressures have an effect on how hard it is for the moving air to displace (raise) the sensor plate, but the adjusting screw simply changes the position of the plunger in the fuel distributor, at a given sensor plate position.

[stormcrow]

The sensor plate lift is controlled by the control pressure regulator.

When the engine is first started, the pressure in the system at the fuel distriutor is low allowing the sensor plate to lift higher allowing for a richer fuel mixture.

As the engine warms up, the pressure on the fuel distributor increases thus leaning out the fuel mixture

The control pressure regulator alows more fuel to flow through it when it is cold and less fuel to flow when it's warmed up. More fuel flowing through it reduces the pressure on the fuel distributor enriching the fuel mixture, less fuel flowing through it increases the pressure on the fuel distributor leaning out the mixture.

You are correct in stating that the adjusting screw only affects the idle.
Hope this info helps.

Steve

"A Porsche does more then just go fast in a straight line"

[350HP930]

The screw will adjust the mixture across al air flow amounts, but its effect is most dramatic at idle.