Quote:
Originally posted by Macel
Well it seems to me like the idle mixture setting isn't quite as important to fine tune - I'd be more concerned if I were leaning it out too much under higher revs.
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I agree. (Except for the emissions test when that comes arround.)
I was quite educated on my ROW 83 CIS. I even did a little tweeking while barrowing an LM1 from a friend. This was a k-basic system without the O2 sensor, control unit, and frequency valve.
Except for in the warm up period (Control pressure lowered)
The mixture is varied, based on air volume, and the 3 different angles in the cone of the air flow meter. In the idle range, the shape of the cone is almost verticle, It then flattens out and near the top it get's steeper again. In addition to this the Control pressure regulator reduced control pressure as manifold pressure increased (Vacuume drops when you mash the go pedal).
When watching the LM1 you could see the mixture changing in relation to these features doing their thing. I have to believe that the initial idle mixture adjustment has an effect on the mixture in the "higher than idle" air flow.
What I saw is the mixture was arround 14:1 at Idle, then leaned quite a bit at light crusing and ramped significantly richer as the rpm increased the air flow and the plate was in that upper (steep) area of the cone. (I recall that that started in the 4000-4500 rpm range and the mixture got as rich as 10-1 near 6000-6500.
Besides those few days I never had the oppertunity to tweek the system further. (I'm not sure it needed it and maybe it was designed to do juat what I saw.) I guess I could have tweeked the system pressure and warm control pressure so that the idle was not too lean while the high end was not too rich. I'm thinking that if I raised the control pressure a bit I could have found that sweet spot.
Now this system was not as sofistocated as the lambda control, but I'm sure Porsche knew that and continued to tweek (hopefully improvements for performance) the k-basic system in the ROW cars until 84 with the Montronic cars.
So, I'm wondering if the basic setting is just as important in these upper rpm / air flow ranges on the lambda cars?