Stalling when braking

[René W]

Since my brakes are done the A is breaking very well,but now the engine is stalling at heavy braking.
I know this is due the position of the main jet in the carburettor(zenith)but is there a solution for this annoying problem?
Looking for a cheap solution,not another carburettor.
Would some kind of baffle into the float bowl be an idea?
René

[Mike V. Florida]

Check here,

https://www.fordbarn.com/forum/showthread.php?t=139880

[René W]

Originally Posted by Mike V. Florida

Check here,

https://www.fordbarn.com/forum/showthread.php?t=139880

Thanks Mike,the carb i have is overhauled and everything is new,the float level is checked and o.k.
Gastank is clean,position of the gav don't make a difference,it stalls enyway.
Me is told it has to do with the position of the jet,the fuel in the float bowl is pushed forward when braking so the jet has no fuel for a while.
If i pull the hand throttle lever down a bit while braking it don't stall,but this is not the way to solve it.

[H. L. Chauvin]

Hi Rene,

After hearing this same Model A engine dying complaint at abrupt stops thousands of times, Mr. Rex Reheis addressed this original Model A Zenith carburetor problem in the book written by Mr. Gordon Bigger.

1. With the carburetor installed on the intake, (while using the improved Dave Renner gauge, accurate within .010"), he recommends very accurately adjusting the float valve with washers such that the washers allow the float gauge to lower the Model A Zenith's bowl fuel level downward 5/16".

2. Ford recommended 5/8" from the carburetor's horizontal meeting metal flange to the top of the fuel level in the bowl; however, in using Mr. Renner's fuel height measuring gauge, Mr. Reheis recommends the distance from the carburetor's horizontal meeting metal flange to the top of the fuel level in the bowl to be 15/16" ..... e.g., 5/8" + 5/16" = 15/16".

[Jacksonlll]

Check for vacuum leak at the connection of the carb to manifold. Make sure both surfaced are flat/ Could also be a small vacuum leak in the manifold.

[HoarseWhisperer]

Sponsored Links (Register now to hide all advertisements)

A worn throttle shaft or bearing resulting in air leak is a common contributor to stalling and easily fixed.

[Big hammer]

Idle speed? A fine line between stalling and grinding of gears!

[René W]

Found it!
The gav rod is a two piece rod,the connection between the two rods was loose so i could turn the knob what i want but nothing happend inside the carb.It was closed the whole time.
Loctite did the trick,thanks to all.
René

[BILL WILLIAMSON]

Some "resolve" the problem by changing the float level, etc, etc.
REMEMBER, it was a COMMON problem, that's why Henry redesigned the float chamber!
Bill W.

[jwilliams81]

Originally Posted by René W

Found it!
The gav rod is a two piece rod,the connection between the two rods was loose so i could turn the knob what i want but nothing happend inside the carb.It was closed the whole time.
Loctite did the trick,thanks to all.
René

Glad you found the problem!
I hadn't heard of a two piece GAV rod before, so I would have been suggesting the float level as well
Put some miles on her now!

[René W]

Originally Posted by jwilliams81

Glad you found the problem!
I hadn't heard of a two piece GAV rod before, so I would have been suggesting the float level as well
Put some miles on her now!

I will do,i use the A as a daily driver,i do about 12000 miles a year

[H. L. Chauvin]

Hi Rene,

With abrupt Model A stops, many Model A owners prevent this Model A Zenith round bottom carburetor "stalling" effect by opening the GAV and/or puling down the throttle to increase RPM's immediately prior to applying the brakes and abruptly stopping.

As mentioned often before, the first 1932 Zenith Model B spherical round bottom carburetor, (like mine), had this same problem as all of the former Zenith Model A round bottom carburetors; however, Ford engineers later changed and modified the float shape and carburetor bowl shape to avoid this spherical "sloshing" effect in later Zenith B carburetors.

The later Model A pot metal Marvel carburetors, (some distributed by Sears), with rectangular carburetor bowl shapes, eliminated this fuel "sloshing and stalling effect.

I like your question in no. 1 above:

"Would some kind of baffle into the float bowl be an idea?"

I often thought of shaping and soldering copper screen to parts of the round bottom of the carburetor to stop the "sloshing" ........ very similar to the effect of "non-sloshing" water in a divided ice cube tray ....... or water transported in a divided egg carton.

I often thought for years that trying to prevent Zenith round bottom fuel "sloshing" for us seniors sounded like a good "Bucket List" experiment. LOL

[René W]

Perhaps some kind of baffle would'nt be a bad idea to create.
For now the engine is not stalling at breaking but the rpm's go down a bit.
I have another zenith laying around and perhaps i'll try to make as you say a copper screen to prevent the fuel sloshing forward.
I'll be back on this
René

[H. L. Chauvin]

Hi Rene,

Also, according to some Model A owners who have monitored carburetor fuel levels when a Model A engine is "not" running vs. when engine "is" running, the fuel level in the carburetor bowl was observed to drop an additional 1/8" when the engine is running at a slow idle.

As one can imagine, to provide a constant flow of fuel when the engine is running, the float has to drop downwards, (in order to supply a constant flow of fuel), to open the float valve above.

With an engine running, with a slightly lower fuel level plus the float moving further downwards, the volume of the space between the bottom of the round float and the bottom of the round carburetor bowl is lessened.

When Mr. Rex Rheis suggest lowering the recommended bowl fuel level, this space between the bottom of the bowl and the bottom of the carburetor is lessened even further which may help to impede the forward "sloshing" of fuel and fuel starvation ....... then increasing engine RPM's may make the bowl drop further downwards which may decrease forward "sloshing" of fuel.

Then with the intake valves drawing fuel from the orifice in the bottom rear of the carburetor bowl, and the fuel "sloshing" forward, the bottom rear of the carburetor is starving for fuel ...... but the intake valves are still getting the same amount of air which makes the engine operate with a leaner fuel mixture.

Also as mentioned further above, leaking carburetor butterflies, and leaking intake manifolds can increase air flow which makes the fuel mixture even leaner during abrupt stops.

Never tried it, but maybe a hollowed out concave rear carburetor bowl fuel reservoir accompanied with a partial screen dam may help eliminate this problem ...... still LOL.

[BILL WILLIAMSON]

Your GAV should NOT affect your idle, if it does, you're idling TOO FAST!
STUDY the carb circuits on MODELABASICS.COM and you'll see WHY!
Bill Slowidle

[Mike V. Florida]

Originally Posted by BILL WILLIAMSON

Your GAV should NOT affect your idle, if it does, you're idling TOO FAST!
STUDY the carb circuits on MODELABASICS.COM and you'll see WHY!
Bill Slowidle

The "Cap Jet" has an additional fuel supply from the "Fuel Bowl". The flow rate of the fuel to the "Cap Jet" is controlled inside the cab with the "GAV" adjustment knob. Turning it left (towards the driver) enriches the fuel mixture for the "Cap Jet". The "Cap Jet" is used at low speeds.

[H. L. Chauvin]

With round bottom Zenith A or early round bottom Zenith B carburetors, both with round bottom floats, before applying brakes for abrupt stopping, some drivers used to turn the GAV to the left, (CCW), to prevent the engine from stalling because of an altered fuel mixture when braking .... also some pulled the throttle handle downwards to increase the idle as they stopped to prevent engine stalling.

Applying brakes to slow down or braking while attempting to temporarily stop when approaching a busy junction or intersection ..... and having one's Model A engine completely stall in any type of busy transverse traffic lane can become most dangerous in today's traffic.

[Beauford]

I have experienced your GAV issue. The top you turn is threaded. Mine was just unscrewing so I was turning and turning and nothing was happening. Yes, Loctite to the rescue.

[JDupuis]

Hey René, glad to hear it running better. Jeff