Motor dies when stopping

[miff]

I have read the posts on this subject . I am running a model b zenith . It was professionly rebuilt. Jets flow tested and installed on an other car ,with any finial adjustments made. I installed it on my motor . Runs fine, but I have to set the ilde on the high side trying to keep it from dieing when I am stopping ( coming to stop sign or hard stop)The gas tank has been boil out and coated, I am running a fuel pump .Reason this is a speedster and the gas tank is in the rear of the car . Tank is vented. All the lines to the carb are new . Pump pressure is two to two an half pounds. It does not over load the carb float.On the gav I run 1/4to 1/2 of a turn.I forgot to state it has a high compression head . Modern distributor ,12 volt system, the reason I when to the b carb was it was my understanding it would elmenate these problems . I have checked and rechecked the timing , points, ect. Is there something I am missing? Miff

[Dollar Bill]

Usual culprit for this problem is low float level. Have you tried raising it a tad to see if that helps? I would also check for vacuum leaks.

[Utopia Texas]

Look at the float level. When you make a stop the gas in the bowl tends to be pushed forward in the bowl causing a temporary drop in the jets which causes engine stumbling. I had this same problem 30 years ago after a rebuild. Adjusted the gas level up a slight bit and the problem went away.

[miff]

Thanks will try the float level adjust and let you know . Miff

[Utopia Texas]

Sometimes the float valve has more than one washer/gasket installed. Removing a excess washer or installing a thinner washer might do the trick. Also check with the upper unit turned up side down that the float is level/parallel to the housing.

[Pilotdave]

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Dollar bill mentioned vacuum leaks - check the gasket between the carb and manifold. I had a similar problem, and we checked all the other possible culprits. The problem went away after replacing that gasket.

Dave

[miff]

Will try that also . Miff

[H. L. Chauvin]

Hi miff,

FWIW: Motor dies when stopping has been discussed as often as Model A Whitewall tires.

(Carburetor float "raising" and "lowering" may confuse some depending on whether the carburetor is held upside down ........... or is bolted-on, and "INSTALLED" in an upright position.)

1. Model A & B Carburetor Restorer, Mr. Rex Reheis, in Mr. Biggar's Carburetor Manual disagrees with the long time Model A Religion (or Heresy), as to "why" a Model A "MOTOR DIES WHEN STOPPING" with a Zenith A and Zenith B round bottom carburetor.

2. He writes that these A & B round bottom carburetors "FLOOD" with "too high" a level of fuel as opposed to "STARVE" for fuel with "too low" a level of fuel in the carburetor bowls; hence, both the carburetor float and the fuel level in a bolted-on & "INSTALLED" carburetor has to be "lowered" to prevent this motor dying condition as opposed to being "raised".

3. On an "INSTALLED" carburetor, Ford recommended a fuel level of 5/8" below the carburetor halves seam; however, Mr. Rex recommends 15/16" below the carburetor halves seam; hence, lowering the carburetor bowl fuel level 5/16" lower than the recommended 5/8" ............... on an "INSTALLED" carburetor.

4. He recommends "lowering" the level of fuel in the bowl in an "INSTALLED" carburetor by adjusting & lowering the float with "additional" float valve washers.

5. As he further described, Renner's sells the best carburetor fuel level gauge tool for measuring fuel level. (Model A parts suppliers sells a cheaper one, that one has to guess at and/or interpolate for the meniscus of the liquid in such a smaller clear tube.)

6. Some Model A owners avoid this motor dying condition immediately prior to stopping by opening the carburetor GAV, and/or advancing the throttle lever a little.

7. I tried Mr. Rex's fuel lowering recommendation on both my A & B Zeniths after witnessing motor dying, and learned that his written "religious" recommendations actually work.

[Capt Quahog]

Sound like the rountine "curse of the Zenith". The handsomely restored Zenith carburetor pulled from our 31' Ford now sits on a shelf having been replaced by a silky smooth running Marvel brand.

[Ed in Maine]

For years I had problems with rebuilt Zenith carbs. I finally got Rex Reheis's book and flow tested jets. Rex gives you the flow data and many hints on rebuilding. You are really wasting your time rebuilding a carb if you do not flow test the jets.

During the flow testing process, I remember Rex had suggestions on how to set up the carb for economy or power. I had my car running perfectly but I was curious what the effect was of changing the flow data on the jets. One of the symptoms I created was a stall as you came up to a stop sign. On some occasions the car would back fire when I let up on the gas and shifted into neutral. It only took a couple more ml of gas flow through the jet to eliminate the problem. So don't forget the role that the jets play in carb performance when solving a stalling problem. Good luck, Ed

[pgerhardt]

Originally Posted by capt quahog

sound like the rountine "curse of the zenith". The handsomely restored zenith carburetor pulled from our 31' ford now sits on a shelf having been replaced by a silky smooth running marvel brand.

x2!!

[miff]

Thank you gentlemen for your input I
Will check my reference books I might have Mr Rex's book. I am going to do the float adjusting. Will keep in touch . Miff

[Bill Goddard]

In your opening post you said your engine was professionally rebuilt. Could it be rough and stiff still? Are you having trouble getting the idle down low enough? Maybe you need more time on it before it smooths out.

[miff]

It was the carb, not the motor. It was redone some time ago.

[VFRhugh]

X3!!!
(Can't control pic rotation)

[Mitch//pa]

A properly rebuilt zenith will not stall and perform well.. ...

[Chuck Sea/Tac]

The model b came with a spring assist float valve, because it was fed by a fuel pump. On an a engine, Gravity feed, you remove the spring. Since you are running a fuel pump, is the spring installed?