After stripping down one of my SU's for rebuild I noticed that there was a rough patch about 1@1/4" x1/2" in the throat of the carb maybe 1" away from the dome and piston area. The rest of the bore or throat is smooth and shiny as it should be but this area is coarse like the surface finish has been eaten away? Wonder what would cause this....no moving parts in that area? A flaw in the casting? Don't think it would affect airflow that much? Any thoughts?