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Don't think In terms of "flats", that's just been a way to describe "turning up" a pump from the position its at. In terms of how far the leaf spring is cranked, in the case of the 90, it should be pretty close to all the way depending on the leaf spring used, however, the difference in the pump from a cranked stocker is all in governor phasing to keep fueling as flat as possible to defuel. The fuel screw just adjusts the peak fueling volume, it doesn't do anything with the curve, that's all determined by the governor assembly.
That being said, are you over fueling? If so, you can turn it down a bit, and should retain its fuel curve.
Currently, I'm getting a tiny puff of black smoke before the turbo spools up when I ham on it, so (for California) I'm pretty happy with the current configuration. That's almost exactly the amount of smoke I was getting before the new IP, and I don't want to attract the enviro-police around here.
My Auber EGT sensor or gauge is acting up and I can't get accurate EGT readings. Assuming my EGTs are under 1250 deg F, I'll keep the fuel screw as is.
As for the IP performance, It runs and idles perfectly. No more surging that I had posted to the forum a month ago. I can't wait to take the van out for some longer trips, to really take advantage of the new IP and turbo kit. Just need to think of something fun to do to the van next.