i had a 1975 450 SEL with the same issues, only the owner replaced the cams because one was worn flat as this engine so often does, he went to the junk yard and bought a set from a 1976 450 SEL that was the first year they went from D-jetronic to the CIS, the cams were different, and caused the exact same issues, we replaced them with another correct set and all was well.