[Schulisco]

Originally Posted by Funracer

You are talking about the CO 3mm mixture screw moving the FD plunger. I have a good understanding of how this effects everything. It affects plunger height in the FD at all times.

I am asking about the AFSP zero position at rest prior to start. This is altered by the 7mm nut and screw underneath the FD inside the air box. Porsche says the edge has to be level with the venturi or up to .5mm below.

After the start the plate floats in the air well above the screw so Im not sure how the “zero position”, as its called in the Bosch book, effects a running engine. My thinking is that the sensor plate height (and really, we are talking about the position of the plunger resting on the arm) effects the initial start for a second or two and then has no effect.

Having said that, the AFSP height at rest IS important. But only to put the plunger in the right place for start. After that the plate moves with the air column.



This screw changes the resting height of the plate. I have moved it all over the place and have never noticed any change in the AFM or how it runs after start except at the very extremes.

My explanation on that:

The lever is not just a simple lever, it's more like a control arm system consisting of two levers. Furthermore both levers are not simply statically 1:1 connected. There is a variable gear ratio being set by the CO / idle mixture screw! Additionally the cone of the funnel also implements a non linear behaviour for the delivered fuel amount. See a picture from the yellow technical instruction to the CIS from Bosch:



The rotating point, where the control arm system hangs in the sensor plate housing is the red marked #8. This point is also slightly out of the center of the fuel distributor plunger to be able to lift it. #5 is a pivot outside that rotating point #8, which movably interconnects the levers #6 and #9. #10 is the counter weight for the sensor plate to balance it's weight for the air draw.
Basically you're right - the CO / idle mixture screw mainly sets the idle mixture. But at the same time the screw also sets a transmission ratio (with narrow limits) for the control arm system! When the air draw moves the lever system, it moves as a single lever. I suppose Bosch was forced to do this to split the mixture enrichment into two parameters to realize the altitude correction: first is the travel of the control lever by the air draw and second is to detect the air density and get it into the equation (which decreases on higher altitude). That transmission ratio is fixed after being set by the idle mixture screw / CO screw.

If now the sensor plate height is out of spec this will also bring the gear ratio of the control arm system out of range - with the consequences I described above.

Thomas