Packard Forum Index » Post-War (1946-54)

Thanks for the thought, but yes, I did watch the timing mark while revving the engine and it does advance as it should, although it could be the vacuum advance doing it. I hear the centrifugal advance rarely goes haywire, and I'm not sure how to isolate it for testing purposes.

The tune-up directions say to remove the vacuum advance.

How's your car doing, if your having problems, this might help if you haven't already checked it out.https://www.packardinfo.com/xoops/html/downloads/Ignition_System_Training_Manual.pdf
Wes

Hey thanks It has a lot of good stuff in it. I have most of the applicable documentation on my Packard but I must have missed this one.
I'm still struggling to figure out what's wrong with my '49. I took apart the carb for the umpteenth time, trying to see if there's something obviously wrong, but everything looks ok to me.

I didn't see anywhere in this thread about the ignition cables. How new, what kind, etc.

I had a similar problem and finally in desperation took the Duchess to the shop that does my Brand X. I had those cables that use newer technology but look like the original black shellac ones. They would not bring the car inside their shop because of "liability issues." So I was thinking, how are they going to diagnose this without hooking it up to one of those big diagnostic octopus machines? (I know now they are no longer used.)

Instead the owner came out with a tester the size of a lunch box. I thought this is a waste of time. If I remember right he hooked up only one wire and ran the diagnostics at the curb. Took about 5 seconds. "It's your ignition cables." I couldn't believe it would be that simple. I got new ones at NAPA across the street. Ran like a top after. I told him that little box was amazing. He said, "Yeah, but it cost $5,000."

Have someone check your cables.

in the document you referenced they describe a simple test of the centrifugal advance by turning the breaker cam. I can turn it but it doesn't turn very much, maybe a few degrees, feels just like slop in the drive gear, is that correct?

A simple test with a timing light as suggested before will tell you if your centrifugal advance is functioning; a distributor test machine is the best way to see if it's properly calibrated. Your comment that it moves "a few degrees' suggests it's functional. If in doubt, as suggested before, remove the breaker plate to see if the mechanism is intact. Photo of a typical centrifugal mechanism from a prewar Delco 662 distributor attached below.

You mentioned you've had the carburetor apart "umpteen" times, did you check the float level and function of the metering rods?

You've received many suggestions on what your problem may be, I'd suggest moving past the centrifugal advance question and on to them.

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Yes, I checked the float level and the metering rods appear to be functioning as designed. There's not much to that carb and I've looked through every little passage I can find to make sure everything is clear.
Regarding the ignition, the centrifugal advance seems to work since the timing mark advances when I increase the engine speed with the vacuum advance disconnected, it's just that the little hand test of the breaker cam doesn't seem to move the way it suggests it should in the documentation. Is it hard to remove the breaker plate? I'm not sure which screws to remove. I know I have to remove the vacuum advance mechanism, but what else?
The problem (rough running) occurs when the pedal is almost to the floor and the revs are pretty high, much higher than the 1800 rpm where the max mechanical advance of 12 deg occurs for the IGT 4203 Autolite distributor, so I guess it can't be ignition come to think of it. I'm really at a loss as to what's going on.

The cables are copper core, at least that's what it says on them. And they look pretty new, although they have little lumps in them which I thought was odd, but I took one off the number one cylinder and watched the spark jump when I held it close to the head. I just figured they were fine.

...so I guess it can't be ignition come to think of it. ..

I think you can eliminate ignition timing, but that doesn't mean it can't be some other aspect of ignition; pretty unlikely with today's preassembled ignition points but "point bounce" (from insufficient spring tension) years back would have been a suspect.

You say this "rough running" occurs at high engine speeds, but it's not clear to me if that means it occurs when revving the engine in neutral, or with the car actually in motion with a load on the engine. If the latter, at what road speed does the problem begin to manifest itself? If the former, what rpm?

What's the history of the mechanical fuel pump? Have you checked the pressure and delivery volume? Does the problem go away or minimize if you engage the electric pump at high rpm?