Model a like a spirited colt or a carburetor problem?

[verrece]

The problem I have is, when the engine is at idle, it looks like a galloping horse, indepently of the best position of the air idle adjust screw. But above 800 rpm the engine runs properly.
After I disassemble the carburetor, I saw that when the throttle plate (butterfly) is closed (in their rest place), it blocks ups a half of the idle hole in the carburetor throat.
Anyone could tell me if when the Throttle plate is closed , the correct position should block the hole completely? or should leave completely open the idle hole? Or as I have now, it should block half the hole?
Could this “half hole blocks” be the cause of the engine gallop?.
The carburetor passageways were cleaned, I followed the Tom Endy´s article.
Any advice will be appreciated.

[RawhideKid]

Mine does the same thing. Lopes like I have a full race cam in it, but I say leave it alone, mine covers half of the hole too, which I think I read someplace is what it's suppose to do.

My wooden nickle worth.

PS. Delete your duplicate post before someone responds to it and you can't.

[Synchro909]

Two things might be causing your "gallop". After going through the carby, check the ignition timing. Too advanced or retarded (I can't remember which) is likely the cause. Your points might have closed up. Maybe experiment a little with it but I'm sure others will chime in.
BTW, we call your symptoms "rolling"

[1crosscut]

While the engine is running spray some starting fluid all around the mating surfaces of the intake manifold. If the engine changes speed you have an intake manifold leak. Be good to eliminate that possibility right off the bat.
Also make sure the carburetor is tight to the intake manifold.

[BILL WILLIAMSON]

The idle hole should be totally OPEN, above the throttle plate.
You're "probably" idling TOO FAST.
Bill W.

[SeaSlugs]

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yea should not "lope" vacuum leak somewhere is my guess - do what cross cut said and spray everywhere. Disconnect the vacuum wiper system from the manifold and plug it somehow too

[Al 29Tudor]

Did the problem start suddenly?
Rich idle can cause looping also.
Is the throttle shaft loose in the carb body and allowing air to be sucked in?

[P.S.]

Does it still do that when the spark lever is all the way up (retarded)?

If it does: Possible vacuum leak. Check around the carburetor butterfly shaft and the intake manifold gasket. Also check vacuum wiper (if so equipped). Or, could be way too rich. Open up the air bleed. If the idle bleed adjustment won't get you there, it could be a blockage in that tiny passage that your butterfly is partially blocking.

If it does NOT: You are running​ too much advance. Assuming you timed your Model A the way Henry specified, your spark lever should only be a few clicks down at idle. The manual that came with your Model A says to run the spark lever about half way down for in-town driving and only all the way down when actually on the highway at highway speed. That, of course, assumes you are running a stock motor with stock head, valves, cam, etc. If you run a high compression head or a touring motor, you need to use even less spark advance or be prepared to go through head gaskets frequently.

Many Model A 'experts' run way too much advance. It is a common mistake.

[verrece]

Thanks for your comments, but I still have a doubt
Is it Bill Williamson right?
Should I let the Idle hole totally open or a half closed?

[katy]

As the diagram shows:

[katy]

Some more info:
http://modelabasics.com/carb%20basics%202.htm

[Big hammer]

The passage way needs to be clean(hole above the plate), when the throttle plate is closed it covers half of the hole and creates a vacuum sucking air and gas!