I'm stumped with a pump

I have a small cast iron, gear pump that was working.

The gear is about an inch in diameter, .375 thick and the other gear (idler
type) is a bit smaller.

No blockages, no clogs, all looks good. However,
there are three set screws/plugs around the periphery of the pump
equidistant at 120 degrees.

This thing no longer pumps but tries to do so.

There are no leaks. I did fiddle with the plugs as it was not doing well.

Help, anyone?

Thanks

j/b


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