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

How much of a vacuum leak should there be coming from the choke stove vent below the exhaust manifold.

Is there a difference depending upon engine temperature? Does the choke vacuum plunger seal and block the vacuum leak once the engine is warmed to operating temperature and the choke is open?

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Since the exhaust manifold itself is never under vacuum, there would be no vacuum leak if the tube was loose. But in fact the choke stove tube should be swedged at both ends so it is air-tight - thus it's merely a passageway thru the exhaust manifold so the choke can pick up heated air.

Thanks for the quick reply.

The tube is attached to the exhaust manifold so that there is no exhaust leak into the stove tube, but the stove tube is open at the end under the exhaust manifold. Thus, the vacuum acting on the choke vacuum plunger is also pulling vacuum past the plunger and through the choke stove tube. This causes a vacuum leak stumble once the engine is hot.

Should there be vacuum through the choke stove once the engine is warm? Is the choke plunger supposed to seal in the down position when hot?

I do not believe that the miniscule amount of air coming through the tube when the choke is warmed up will cause a stumble. When the choke piston is at the bottom of its bore it closes off most of the air as I recall, when cold more air comes through to heat the choke spring. As far as the stumble, check engine vacuum at idle, should be 18/19 or so.

Stumble is likely the vacuum advance, check it. Also check operation of accel pump, gas should squirt out of both nozzles.

Let us know what you find.

Thanks.

The stumble is only at idle, the car drives and excelerates fine. It appears that the choke vacuum plunger must not be seating correctly as I have much more than a minuscule leak at warm idle. I can block the end of the choke stove and the idle stumble completely goes away.

I expected a litle vacuum leak at cold idle to pull the heat through the choke stove, but I didn't think there should be any vacuum loss at warm idle, but since I am a novice Packard mechanic, I was not sure. Thanks again.

G'day Terry S,
to PackardInfo. I invite you to include your Packard in the Packard Owner's Registry.

A Packard always ran flawlessly whether cold or hot if everything is adjusted and operation properly. At idle poor running might be best described as a "rough idle". A stumble usually describes an attempt to move and a difficulty as when first accelerating and the car misses and runs poorly for a few seconds.

Terry, Checkout this link on how a carburetor works:packardinfo.com/xoops/html/downloads/49_CarburetorTrainingBook.pdf
Wes

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Thanks everyone for quick replies.

Disconnect the tube fitting from the choke housing and put your finger over the hole and see if it's leaking/pulling vacuum while running?
It should not.
If leaks, time to rebuild carb.
If the tube is passing exhaust, the tube is rotted inside the manifold and needs replaced. Takes a bit of work but can be done. I replaced one.
The choke tube is only supposed to transmit warm air to the choke spring to allow it to expand and change the position of the choke plate. Once it's hot and fully open, it won't matter unless improperly adjusted.
ps: Make sure the spring is not in backward, it's easy to do and won't open.