1983 300D

When warmed up I'm hearing a clack, clack, clack at idle & it's rhythmic with the engine. I've adj. the valves & I have the lubro moly comming in the mail. Injectors have approx. 55K on them.

I bled out all the injector lines & seems #3 keeps getting air in it. Yet I don't have any fuel leaking or even seeping.

Any ideas where to look?

Thanks for any help in advance...

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1983 300D 285,000
1948 willys fuel injected, tons, 39.5 PBR's
2000 PSD pumped for pulling..