My initial approach of cleaning the injectors was to close those openings, which I did not want (e.g. with coins and heat-glue), then I put quite a bit of carby-cleaner (Carburetor-cleaner) into the rail, and while carefully applying airpressure (via air gun) into the rail, I attached 12V to the injectors (one after another). At 6 of the 8 the spray-pattern looked alright. I was a bit worried about the other two, which where highest up, when positioning the rail on the ground... - maybe it was o