I've put in a new hand primer pump in 2 other 240D's I've had- I just unscrewed the old one and screwed in the new one... I thought that was all there was to it...
but
I've recently acquired another 1977 240D and have been fixing up small bits and whatnot- I went to swap the leaking old style hand primer pump with a new bosch and when I unscrewed / removed the old one there was a little plunger & spring still sitting in the exposed hole.. ??!! What are these parts? are they supposed to be in there? the other 2 cars I've done this to never had anything sitting in there, just an open fuel line that I screwed the new primer pump to.

I haven't seen any other posts/ tutorials mention anything like this so I'm confused..

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1981 240D ... 265k
1977 240D ... 265k
1977 240D ... 250k