Engine vacuum holding throttle open?

What would cause this? With the engine running the throttle plates are very stiff and require quite a bit of effort to close. Turn off the ignition and they return to normal. The car has an unintended acceleration problem because of it.

This is on a '34 Packard 12 with the original Stromberg EE3 carburettor so there are no systems that could be interfering. The carb was rebushed recently so there is no excess play in the throttle shaft.

This one has all of us scratching our heads, so I turn to the GRM braintrust.

What kind of vacuum readings do you get?

Missing a return spring someplace?

Hmm..

The one we just finished has a very light return spring and stays shut on it's own when running just fine.

Is it possible that the throttle plates are installed upside-down on the throttle shaft?

Hey, something else just occurred to me.

Have you messed with the automatic choke? it has a small vacuum operated plunger in the heater assembly at the front of the manifold, maybe something is screwy in there and is pulling the choke closed a bit and, because they're linked, pulling the throttle open.

Could the hand-throttle control tube be binding up in the steering shaft?

We just finished out Packard Twelve and I'm the guy who rebuilt the carb and freshened up the engine and ours is working great. If you want, PM me and I can send you pics of our carburetor coming apart and maybe going back together. Or you can send me some pics of your carb and I can compare it to ours.

Whatever you do, don't break anything on the EE-3 carb, they're made of unicorn horn.

Shawn

Assuming is free to move with the engine off is Vacuum force on throttle plate is causing it to bend and bind in the new tighter bushings?

I would be inclined to suspect vacuum pulling the external shaft seals, creating a vacuum induced bind. I've seen similar on things like old Ford tractors.

In theory vacuum should close the throttle plates. In every carb and throttle body I've ever seen, the throttle plates are offset slightly so the part that opens away from the engine has more area, therefore vacuum helps pull it shut.

Note that I've never worked on one of those prewar carburetors, so I don't know if this was practice from time immemorial or some newfangled idea they came up with between Then and Now.

foxtrapper wrote: I would be inclined to suspect vacuum pulling the external shaft seals, creating a vacuum induced bind. I've seen similar on things like old Ford tractors.

hey ... welcome back .. how ya feeling ?

Hum....Did the carb rebuilder pull the throttle plates out the shaft to re-bush the main body? If so they might have installed them backwards the plates are offset just a wee bit to make sure vucuum closes them.

Trans-Maro had it on the money. The clock spring in the choke control mounted to the intake manifold is broken. The Choke never closes. Push it open and the throttle plates act normally.

It's a goofy automatic choke isn't it?

The only folks who would know about it have probably worked on a Packard.

Post some pics when you're all done, I'd love to see it.

I've also got a fair bit of documentation here, If you can give me the serial number from the firewall data tag, I can probably tell you who it was sold to first and where it was sold. I might be able to tell you where in the production it sits as well.

Shawn

I will get that tomorrow. That would be cool

GRM: Uniting Packard Restorers since 2013!