'55 352 stumble

[55Connie]

I'm a newbie to this post, and I have an old problem I'd like to run by y'all.

My '55 Connie has a 352 single 4V, which is original (never been opened up) with about 62,000 miles from new. Compression is good and even, and I have an oil pressure gauge fitted, and that is strong too. I did replace the timing chain when I did the water pump, and it was loose. The fuel pump is also rebuilt.

It takes forever to fire up, and it has an annoying off-idle hesitation: when it's cold it's enough to cause it to stall, which is not fun. It also surges at steady part throttle. I've rebuilt the carb twice, the distributor and timing seem correct. I've searched high and low for a vacuum leak, because I'm sure that's the problem. It's better when warmed up but still not right.

The Treadle Vac seems to leak vacuum, but I'm not sure if that's normal or not. It too has been rebuilt twice, and I don't know how to make it not leak at least somewhat. It works fine, and I assume that the vacuum reservoir is there to help it along.

The vacuum wipers are blocked, the vacuum lines to the reservoir are good, and the tank holds suction. The washer lines are unplugged and blocked too. I have a small electric fuel boost pump added to the line that I use for cold starts.

Any ideas? I'd sure like to make that problem go away.

55Connie

[Guest imported_PackardV8]

The treadle vac mite make a little bit of a hissing noise when pedal is depressed but should be quite when foot is not on pedal. There is a 6" piece of hose INSIDE the treadle vac too that mite be leaking.

[Guest imported_Speedster]

Have you tryed disconnecting the Vacuum lines to brake-booster, distributor, etc. and Pluging them, to see if it runs better?

[Guest imported_Speedster]

I found a vacuum leak in an unusual place on my '56 Clipper.

The choke-heat-riser tube, that goes thru intake-manifold was leaking at lower end.

It goes thru a hole in bottom of manifold as well as the hole you can see on top side. (where tube for Carb. choke goes)

I had to remove Intake manifold and flare out the tube with a round tapered punch, to get it sealed. I think the tube had rusted enough to cause the leak.

The next time I have the Intake off, I think I'll try to replace the tube.

[WCraigH]

55Connie:

If temporarily blocking all the vacuum lines doesn't remedy the problem:

Do you have the WCFB or the 4GC? The latter has a off-idle power system that may be blocked or otherwise inoperative. Both have an accelerator pump system that if it has slop in the throttle-to-pump linkage will also cause an off idle stumble. My 55 Pat's 4GC had this problem. I used JBWeld to close up the linkage holes and redrill to the original size: no more stumble.

You might also check the thermostat valve in the driver's side exhaust manifold. It may be rusted/jammed open. This would significantly delay cold start manifold heating. My 55 Pat also had this problem. As a matter of fact, some prior owner had completely removed the internal valve! I replaced it with a NOS one and this helped cold start warm up a lot.

[55Connie]

Thanks, guys: this is the kind of thing I needed: someplace specific to look that requires specialized knowledge!

The hose inside the Treadle Vac is good, and it does not hiss when not depressed.

The heat riser in the exhaust manifold is free and working.

Blocking all of the vacuum taps makes it run a lot differently: idle speed goes way up for example, but it still doesn't drive correctly that way. (And it's very scary without boost on the brakes!)

The carb is the Carter, and I'll check those items, as well as the heat tube.

55Connie

[Guest imported_Speedster]

I would determine which vacuum line is making the Idle speed increase, plug that line or determine where the leak is and then adjust needle-valves on Carb until the idle speed is correct. (someone probably had to adjust carb fuel flow to compensate for excess air from leak, to get it to idle)

[Guest Albert]

Are you sure you are not off a tooth on the camshaft timing, as it will do the same thing as well you describe. How was it running before you changed the timing chain?

[55Connie]

I'm still figuring out the avatar image thing, I'll see if I can fix it.

One of the things that's most frustrating about it is that I'm usually pretty good with engines, and I've done just about everything I can think of. Replacing the timing chain made NO difference. A completely rebuilt distributor made NO difference. I rebuilt the carb, then had a professional shop do it, and it made NO difference. Completely blocking all vacuum ports made a big difference, but it was not right or 'better', just different. I did readjust the timing and idle mixture screws to suit, but the power was way down, and the stumble moved up the rpm range.

It has all the classic signs of a vacuum leak, but I'll be darned if I can find it. I tried a hose to the ear to listen for a hiss under the intake ports. I sealed the carb base at least 3 times.

Maybe it's a function of it's age, so that pipe idea is a good one I wasn't aware of. My '57 BelAir had a similar pipe in the exhaust manifold, and it leaked until I reflared the end.

I know modern condensers don't hold up too well these days, and a weak spark could be an issue. I've changes all of that stuff twice.

Every other Packard V8 I've seen runs beautifully. It's driving me nuts! I don't drive it much as a result, and I really needed some experienced hands to help me work it out. I'm going to go down the list you folks have provided, leaving no stone unturned. Thanks for all of the good suggestions, I'll keep you informed.

55Connie

[joe kastellic]

You say that blocking all the vaccum ports made a big diffrence in the idle it went way up can you block one at a time and try to see which one affects the change in your idle speed, this might be one way to go. IF you put a rag over the carb does the car still run or does it die? what color are your spark plugs? are they all the same or are some diffrent colors? DO you have access to a vaccum gauge? what type of reading do you get at idle? is it steady or is erratic? how many inches of vaccum? Joe