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I installed a rebuilt AC fuel pump with new material (neoprene) diaphragms in my 1954 Packard Super Clipper 327ci L-head 165hp 8cyl. The old rubber diaphragms in the original fuel pump were deteriorated. The engine idled roughly with the old fuel pump and it still idles roughly and occasionally stalls in traffic when I release the accelerator pedal and use brakes to stop. I have played with the idle adjustment screw and that does not seem to help much. I have noticed that the flexible fuel input line to the pump seems slightly worn and brittle with age. Might this be the culprit or is there something else in play, perhaps involving the carburetor? Thanks for your thoughts.

steve828, It would be a good idea to replace fuel pump flex hose now - new pump, new hose. Your rough idle and stalling may be caused by an improperly adjusted or flooding carburetor. You say you have tried adjusting the idle speed, have you tried to adjust the idle mixture? There are two brass, round headed screws that are the idle mixture jets at the front bottom of the carburetor. With the engine idling as close to the specified idle RPM as possible turn in one screw until the engine starts to run rough, then back out about one-half turn. Do this on the other jet and go back and forth until you get a good smooth idle. You may have adjust the idle speed adjustment during task. If you can screw in the idle mixture jets all the way (don't force them, just until you can feel them bottom) then the carburetor is flooding and is getting gas from the flooding to keep it idling even with the jets screwed closed. Others may have other suggestions to help you solve this problem.

(o{I}o)

There are a number of things which could cause the rough idle problem but I would not put the the fuel pump near the top of the list especially since the fuel pump rebuild did not improve the situation and the car is otherwise running OK. The carburetor may just need adjustment so I would start there as you suspect. Here is the link to the 1951-54 Packard factory manual. I suggest that you download it and read the relevant sections .
https://packardinfo.com/xoops/html/modules/article/view.article.php?4
A few basic tools such as a compression tester, tach/dwell gauge and vacuum gauge are invaluable for diagnosing problems and adjusting these engines if you don't already have them.
Let us know how you make out.

I suggest you get a factory service manual ofr your car, or really use one for any car of the era. Most have diagnostic sections as do Motors Manuals. Instead of a "guess" system, make use of information produced by people who knew cars of the era better than most of us ever will.

Cars are logical animals, treat them as such.

I'd suggest starting with a compression test and check the manifold vacuum. If the #s are good then a good, thorough tune-up. If you don't know the last time a good, thorough, deep tune-up was done, it's been too long.

Thanks to all for all your suggestions. Adjusting the idle set screws seemed to help quite a bit. When the car has been driven and warmed up, the idle seems to get a bit less smooth but overall a big improvement.

It's a good day when a little adjusting cures the problem. Maybe a tune up is in order (points, plugs, cap, rotor etc.)?