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Old 10-27-2012, 10:23 PM   #1
TreeTopFlier
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Default zenith carb baffles to prevent stalls during braking

So I've rebuilt the carb to the best of my abilities... a Zenith II.

I still ever so often get a stall when I come to a stop.

Has anyone come up with a baffle for their carb bowl to prevent this from happening?
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Old 10-27-2012, 10:38 PM   #2
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Default Re: zenith carb baffles to prevent stalls during braking

I've thought about a baffle, but never pursued it. Bill W.
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Old 10-27-2012, 10:43 PM   #3
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Default Re: zenith carb baffles to prevent stalls during braking

My carb does the same thing if I brake fairly hard (which is normal braking for many modern driver's). Just pull the throttle lever down a notch or two while braking.
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Old 10-27-2012, 10:49 PM   #4
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Default Re: zenith carb baffles to prevent stalls during braking

This web site has excellent troubleshooting for carburetor rebuild and troubleshooting.

http://www.modela.org/
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Old 10-27-2012, 10:54 PM   #5
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Default Re: zenith carb baffles to prevent stalls during braking

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Originally Posted by Tom Wesenberg View Post
My carb does the same thing if I brake fairly hard (which is normal braking for many modern driver's). Just pull the throttle lever down a notch or two while braking.
Yes I've noticed it hardly ever does it unless I'm coming into a stop over speed. I first noticed it when I was trying to located a drag in my brakes.

I hear from many veteran A drivers that this is a very common issue, all of whom all say to pull down the throttle a few notches to prevent it when needed.

I've got to bet theres someone out there who has hands off trick to prevent the carb from stalling out as well.
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Old 10-28-2012, 03:16 AM   #6
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Default Re: zenith carb baffles to prevent stalls during braking

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Does it help to open your GAV a quarter turn?
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Old 10-28-2012, 03:18 AM   #7
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Default Re: zenith carb baffles to prevent stalls during braking

Try increasing the float level when you apply brakes you are pushing gas forward in the bowl I raised my level and stop this
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Old 10-28-2012, 08:50 AM   #8
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Default Re: zenith carb baffles to prevent stalls during braking

Lowering the float a small amount will usually solve the problem. Lowering the float reduces the amount of gas in the bowl that sloshes first foward and then back when the car comes to a stop and floods the engine. I keep an assortment of gaskets that fit under the float valve assy. adding a thin gasket as a shim lowers the float valve and changes the float level.
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Old 10-28-2012, 10:51 AM   #9
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Default Re: zenith carb baffles to prevent stalls during braking

After the last carb rebuild, where the proper size jets were installed, the car doesn't stall on hard stops, or ANY stops anymore. It's just super smooth and reliable now.
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Old 10-28-2012, 05:47 PM   #10
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Default Re: zenith carb baffles to prevent stalls during braking

#7 says increase flat level, #9 says lower the float level................
Which is it??
Paul in CT
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Old 10-28-2012, 06:45 PM   #11
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Default Re: zenith carb baffles to prevent stalls during braking

Thanks Vince ! ! !

Paul in CT
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Old 10-28-2012, 07:01 PM   #12
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Default Re: zenith carb baffles to prevent stalls during braking

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Originally Posted by fordgarage View Post
From years ago, my experience is that there are three potential causes.

1) Improper float level. How did you measure yours?

2) Dirty carb passageways. How do you know yours are clean inside?

3) Battery cable insulation worn where cable crosses on the brake pedal rod. Brake application causes intermittent short which tries to kill the ignition. This is more common than you might expect. Check it out.

Stalling on braking is not a given quirk of the Model A design.
The car will not behave like this unless something is wrong.
Very happy to hear your can do attitude on the stalling... I am determined to address it.

1) sight tube gauge from snyders

2) fully rebuilt carb using adams instructions, used aerosol carb cleaner and a paperclip for all "secret passageways"... they were free at least free and flowing then (measurable?)

3) good idea, but that did cross my mind and I added extra shrink tubing to possible wear points when i first noticed that potential

back to 1, if i set mine at 5/8" below gasket surface... would you recommend i bump up or down the float setting?
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Old 10-28-2012, 08:12 PM   #13
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Default Re: zenith carb baffles to prevent stalls during braking

The Dog just called me to the pendulum clock and barked, barked, barked,----- Oh! I see, just firmly affix a lead pendulum weight to the carb lever and when stoppin' HARD it would advance the throttle! Amazing Dog! Send treats in c/o BUSTER T. Brown Bill W.
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Old 10-29-2012, 06:57 AM   #14
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Default Re: zenith carb baffles to prevent stalls during braking

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Originally Posted by fordgarage View Post

Stalling on braking is not a given quirk of the Model A design.
The car will not behave like this unless something is wrong.
True!

"Life is too short to put up with stalling carbs".
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Old 10-29-2012, 09:24 AM   #15
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Default Re: zenith carb baffles to prevent stalls during braking

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Originally Posted by TreeTopFlier View Post

back to 1, if i set mine at 5/8" below gasket surface... would you recommend i bump up or down the float setting?
Keep it at 5/8" and look elsewhere. Several years I experimented with the float level on my Fordor which was already running fine. I test drove it (hard) with the float level both higher and lower than normal and there was no loss in performance and no stalling on very hard braking. I'd be shocked if simply a change in float level would ever solve the stalling issue.

Twice I've encountered the issue with stalling when coming to a stop and in both cases it was solved by readjusting the idle mixture. I don't recall which direction for sure but I suspect I opened it up to lean it slightly. I can say however that I adjusted it until the idle speed started to slow and then increased the speed slightly with the lever stop screw, still maintaining a nice slow idle.

I wrote a similar description to the same question here sometime back but the person asking the question never reported back.
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Old 10-29-2012, 10:52 AM   #16
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Default Re: zenith carb baffles to prevent stalls during braking

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Originally Posted by Marco Tahtaras View Post
Keep it at 5/8" and look elsewhere. Several years I experimented with the float level on my Fordor which was already running fine. I test drove it (hard) with the float level both higher and lower than normal and there was no loss in performance and no stalling on very hard braking. I'd be shocked if simply a change in float level would ever solve the stalling issue.

Twice I've encountered the issue with stalling when coming to a stop and in both cases it was solved by readjusting the idle mixture. I don't recall which direction for sure but I suspect I opened it up to lean it slightly. I can say however that I adjusted it until the idle speed started to slow and then increased the speed slightly with the lever stop screw, still maintaining a nice slow idle.

I wrote a similar description to the same question here sometime back but the person asking the question never reported back.
Marco I have never gotten muchnoticeable finetune-type of adjustment out of fiddling with the idle mixture, contrary to what the service bulletins state. Do you think that since gasoline back then was of poorer quality that minor carb adjustments back then were more perceivable?
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Old 10-29-2012, 10:56 AM   #17
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Default Re: zenith carb baffles to prevent stalls during braking

have you tried a different carb? or two?
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Old 10-29-2012, 12:12 PM   #18
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Default Re: zenith carb baffles to prevent stalls during braking

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Originally Posted by ericr View Post
Marco I have never gotten muchnoticeable finetune-type of adjustment out of fiddling with the idle mixture, contrary to what the service bulletins state. Do you think that since gasoline back then was of poorer quality that minor carb adjustments back then were more perceivable?

In my experience when I cannot get a change in the performance with the air idle adjustment I have found that the passage in the air idle circuit has a partial blockage. Thus resulting in no change from adjusting the air idle screw as the passage block is controlling the volume of air, not the air idle screw.
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Old 10-29-2012, 12:33 PM   #19
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Default Re: zenith carb baffles to prevent stalls during braking

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Originally Posted by ericr View Post
Marco I have never gotten muchnoticeable finetune-type of adjustment out of fiddling with the idle mixture, contrary to what the service bulletins state. Do you think that since gasoline back then was of poorer quality that minor carb adjustments back then were more perceivable?
I'm assuming from the question that you do get a variation but not enough improvement. That would be due to other issues such as (but not limited to) air leaks and improper jet sizing.
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Old 10-29-2012, 01:33 PM   #20
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Default Re: zenith carb baffles to prevent stalls during braking

Had that same problem (no difference with idle adjustment) on a ebay bought "professinally rebuilt" Zenith carb. This is a guy that sells a bundle of carbs he rebuilds on ebay, and is supposed to be one of the "experts". The jets were wrong, and the car did stall at stops. After having the "new" carb rebuilt by someone who actually knows what the Zenith is supposed to look like, the car runs like a swiss watch. Never stalls, no matter how quick the braking or jerking around. It's just a rock-solid running car now, feels like a whole new motor.
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