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Well, I'm at my wits end over this. About a month ago I noticed my '49 Custom 8 started to run rough when I opened the throttle. It starts to accelerate and then when the pedal gets to about 3/4 to the floor the engine bogs down, it stops accelerating and runs rough. Prior to this it ran fine at all speeds, even at freeway speeds around 75 mph or higher. This is what I've done thus far:

replaced the vacuum advance on the Autolite distributor
replaced the points
replaced the condenser
replaced the coil ( there's a separate post on this in this forum)
replaced the fuel pump
replaced the inline fuel filter off the tank prior to the electric fuel pump ( I never use the electric fuel pump, no need to, I drive the car almost every day)

I set the points at .016.
The plugs look ok, a little sooty, but it runs a little rich.
I rechecked the manifold vacuum and it's a steady 19 inches at idle ( I'm at about 1300 ft above sea level here in southern California). And when I blip the throttle it behaves as it should, dips and then comes right back to 19 inches.

I did a compression test and the pressures were a bit low ( in the mid 80 psi range but consistent across all cylinders.)

I checked the ignition timing and it's right on at 6 deg BTDC, vacuum advance disconnected.

I took apart the carb (Carter WD-O 531SA). I didn't rebuild it because I don't see anything wrong with any of the components that typically come with a rebuild kit. The needle and seat look fine, the accelerator pump looks ok and seems to pump ok. I took out every brass orifice making sure they weren't blocked. I sprayed carb cleaner through every passage I could find. The metering rods appear to operate as designed and they look ok.

I had a very similar problem with my '50 Ford a few years ago and it turned out to be the coil. There were some posts in this forum ( or maybe it was somewhere else, I can't recall) that said you had to be carful about coil polarity so I took the coil off my Ford (also positive ground system) and put it on the Packard and I still had the problem.

Up until this time the car ran perfectly, although around the same time I noticed some tapping noises ( I posted that on this forum also) but nothing really bad, and it goes away after about 10 or 15 minutes of driving.

What could it be???

Below is the trouble shooting for loss of power, just remember that just because some thing is new doesn't mean it is good. Also make sure you have good air flow going into the engine and also coming out.
Wes

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It might be worth a quick test without an air cleaner to see if that would have anything to do with the problem.

I have never paid attention to what is in the chamber or silencer behind the filter element but more than one of the old Gus stories had a theme of some kind of baffle or silencing material in air cleaners loosen. When whatever item was free to move and the engine was needing to pull a lot of air at higher speed the item could shift and partially block airflow with results similar to what you describe.

Thanks for the input. It's the same when I remove the air cleaner.

Another hard to find and weird problem with high speed operation was if for some reason the oil pressure increased over the normal maximum, then at sustained higher speeds any weak valve springs would let lifters pump up to the point those valves did not close tightly. When the oil pressure was back in proper range the lifters reverted back to their normal bleed down and all was well again.

Can't really see that happening but since you have looked at all the usual and do have hydraulic lifters, it might be worth looking at weird. Verifying with a known good gauge if the oil pressure is stable and staying in the same range as when the engine is OK would be easy enough to do. The pressure regulator valve could have started sticking or acting up.

Have you checked to see if the mechanical advance is working?

Find someone with an old SUN dist. machine and have them test it. I find that when there is no mechanical advance the engine starts to give up at about 45-50 MPH.

A quick check is to watch the timing mark on the vibration damper with a timing lite while someone revs the engine, you should see the timing marks advance.

If you suspect a mechanical advance problem and can't find a SUN machine contact me as I have one, and am willing to help out.

Sincerely, John

Loosen or remove gas cap and try again.

Also need to open up the points to .018.

At this point i will not go into alot of detail.
I've had a similar problem with a 2.0 Ford 4cyl. It turned out to be somekind of a wax or parafin building on the EXH valves on the TAPPEt side of the valve stem.

I wuit running the convenient local Marathon and (by sheer hapenstance) began to run Shell. Problem 90 % solved in less than 3 tank fulls.

Again i'm leaving out alot of detail and direct analysis and actual cleaning of the valves with a wire brush that took place over a period of about 4 years that this sticking exh valve problem had existed and only got WORSE over the 4 years.

Just to be sure, does the Vacuum Advance need to be removed disconnected and plugged when checking timing? If you look in the tune-up manual it doesn't say anything about removing it or did I miss something? I've always done it on newer cars with the rubber hose, but what about the hard line vacuum advance?
Just asking.
Wes

Oh, another one of the old Gus stories was a collapsing fuel line going to the fuel pump.
Wes

Several other things already mentioned that should come first but don't ignore the function and adjustment of the metering rods.