I have a 1968 200D with the OM621 engine and floor shifted 4 speed manual. I know these cars are supposed to be slow but my car loves to cruise at 40mph all day long. It doesn’t get up to 60mph unless I’m going down hill or I have a really really really long and flat straight away. Just seems like it should have a bit more power. Is there a fuel delivery adjustment screw on these injection pumps? Any help is greatly appreciated