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Old 03-12-2018, 12:51 PM   #1
jgusgann
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Default Zenith carb stall

I have rebuilt my zenith, new jets, throttle butterfly axle, float. I have replaced intake/exhaust manifold gaskets, checked wiper connection.
But still when I brake, car wants to stall. I'm having trouble engaging idle circuit.


I'm thinking of just removing the secondary well, thinking it may be hindering fuel flow from fuel bowl.. I also noticed that my gas cap may be air tight preventing fuel flow to the carb. After this I'm out of ideas.
Any other suggestions?
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Old 03-12-2018, 12:57 PM   #2
TinCup
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Default Re: Zenith carb stall

Sounds like the float may be too low. This is a common issue on the Zenith carb which is why in 1932 the float design was changed so that the float was perpendicular to the car not inline. When you are braking you are changing the level of the float. You can be starving the car for gas when you brake hard. Lots of things to check here.

1. Does the car idle well?
2. What is your GAV setting when driving?

If you gas cap was not venting it will have trouble running anytime. Drive it around with it off and see what it does. Try opening the GAV another quarter turn and see what that does to your stalling.

Removing the secondary well is not the solution.
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Old 03-12-2018, 01:08 PM   #3
Tom Endy
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Default Re: Zenith carb stall

The small hole in the throat of the carburetor may be plugged. This is the idle passage. The way to check it is with air pressure. Remove the idle jet and put the air nozzle against the idle jet hole and blast it while holding your finger over the hole in the throat. You should feel a strong blast of air coming out of the hole.


If it is plugged it is possible to get a paper clip in through each end to clear the passage way.


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Old 03-12-2018, 01:28 PM   #4
Al 29Tudor
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Default Re: Zenith carb stall

I have cured this problem by adding a second gasket under the float valve to drop the level in the bowl.
Seems counterintuitive but it I've seen it work twice.
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Old 03-12-2018, 02:43 PM   #5
jgusgann
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Default Re: Zenith carb stall

Quote:
Originally Posted by TinCup View Post
Sounds like the float may be too low. This is a common issue on the Zenith carb which is why in 1932 the float design was changed so that the float was perpendicular to the car not inline. When you are braking you are changing the level of the float. You can be starving the car for gas when you brake hard. Lots of things to check here.

1. Does the car idle well?
2. What is your GAV setting when driving?

If you gas cap was not venting it will have trouble running anytime. Drive it around with it off and see what it does. Try opening the GAV another quarter turn and see what that does to your stalling.

Removing the secondary well is not the solution.



Hey terrific reply Tin Cup!! I do notice that when I brake and come to a stop, it does seem like the idle surges as if it just got gas. In fact, when I start to stop, I can sort of tap the brakes to slow down and the idle seems to respond to that, ie surging effect.


But I really don't see what the secondary well does for the carb. It seems to me its just a smaller tube inside a larger tube.
I'll play with the float level, great suggestion thanks!!
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Old 03-12-2018, 02:51 PM   #6
jgusgann
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Default Re: Zenith carb stall

Tom Endy- no, the port hole is clear, checked by blowing on Idle jet and close off idle air adjust screw ... by the way, very excellent manual on the zenith, have read over it many times.


Al 29 Tudor- interesting suggestion and will try and yes does seem counterintuitive.
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Old 03-12-2018, 03:54 PM   #7
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Default Re: Zenith carb stall

Quote:
Originally Posted by jgusgann View Post
... I really don't see what the secondary well does for the carb. It seems to me its just a smaller tube inside a larger tube.
The brass secondary well is to reduce the idle jet getting fuel surge ( too much or too little) on a sudden stop.
PS does the car idle OK normally? .. . "90% of carb problems are electrical ! "
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Old 03-12-2018, 03:54 PM   #8
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Default Re: Zenith carb stall

I'm putting my Zenith-1 together tonight so maybe i'll be adding to this in a few days.
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Old 03-12-2018, 04:10 PM   #9
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Default Re: Zenith carb stall

I've always found that when the engine dies when braking, it is either a leak somewhere around the manifold or the float level is too high. Seems wrong and it took me a while to accept it but the guy who told me was right.
So, what to do? You say the manifold is sealed up tight but I'd still check it. With the engine idling, spray starting fluid around it and listen for a change. If that is all OK, try putting a washer under the float valve, thus lowering the fuel level. Go for a drive and test it.
Please report back when you get it right so others can learn what works.
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Old 03-12-2018, 06:42 PM   #10
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Default Re: Zenith carb stall

Here is a link to some information on the secondary well.

There were 4 secondary wells produced and if you have the wrong one you can affect the flow of fuel into the secondary well. The way to check is to remove the compensator jet and see if the boss on the secondary well is interfering with the flow of fuel to the secondary well. Remove the compensator jet and take a pencil and through the compensator jet hole mark the secondary well, remove the secondary well and if the pencil mark is on a boss it is affecting fuel flow. To correct the problem either replace the secondary well with one that does not impede fuel flow or put two gaskets on the compensator jet.


http://www.modela.org/secondary_well.html
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Old 03-12-2018, 08:23 PM   #11
Gary WA
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Default Re: Zenith carb stall

Float!!!! Adjust!
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Old 03-12-2018, 08:31 PM   #12
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Default Re: Zenith carb stall

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Float!!!! Adjust!
Yep. It is almost always the float.
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Old 03-12-2018, 08:33 PM   #13
jgusgann
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Default Re: Zenith carb stall

well folks, the verdict is definitely in. After suggestions to lower the float I went straight home after work, took the carb off, put one additional washer under the float valve, put it right back on the car, let it warm up few minutes, and off for a test drive.
I could pretty much tell right away before I took off that it seemed to be idling better.
Sure enough, brake after brake after hard brake, and near perfect idle!! Not even slight or almost stall!! I can hardly believe it.

Thanks to Al 29 Tudor, Synchro 909 and others... a great suggestion that I would not have arrived at on my own!!
And the explanation about the function of the secondary well (as to why to NOT take the brass secondary well out) was really helpful and made a lot of sense to me. Thanks Johnbuckley and 160B!!!
What a great forum!!!
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Old 03-13-2018, 04:44 AM   #14
johnbuckley
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Default Re: Zenith carb stall

I find the viton tipped float valves usually need two gaskets ( even 2 1/2) to get the level right.
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Old 03-13-2018, 06:07 AM   #15
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Default Re: Zenith carb stall

A vacuum leak can cause this too. When you redid your carb, I hope you made sure the two surfaces were flat. Put a file to both the manifold flange and the top of the carb to make sure they are flat. For the manifold, use a mirror and a light. Not a bad job. A leak in your manifold could also be the problem.
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