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  #1  
Old 11-17-2022, 05:43 AM
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Location: Rockford IL
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Setting Zenith Float Height

I am trying to make sure that what I am doing in the float chamber of my Zenith 35/40 INAT carbs is correct.

At this time the carbs will idle wonderfully, but stumble anytime fuel is given. I cleaned the carbs, replaced the acceleration pump and made sure the float was not sticking. I did not go thru a full rebuild at this time, I am just trying to get the car running before winter.

What I know about these carbs is strictly from what I get from you Gentlemen and what I can pick up from the internet.

When I disassembled the the carb, the front float valve was stuck, the (needle/ jet?) was protuding from the bottom of the float valve itself. I had to soak it in SeaFoam and tap it back and forth to free it up. I figured that protrusion was normal.

After the second start up without much improvement, I pulled one of the new float valves from the rebuild kit and I find there is no way to push that needle below the bottom of the float valve. So there is a problem.

One thing i need to understand is how that valve works. There is no spring that I can feel, is there a small piston in the valve? What raises the needle while in operation? It has to have contact with the float assembly to regulate the fuel in the chamber and it sits in a vertical position, correct?

I was looking at float valve height settings on an internet document on the 35/40 and it mentioned there were two types of valves with different float settings. One with a spring and check ball and one without. I am guessing the one I have pictured has no spring? This information came from an old 35/40 document from a BMW Database.

I will probably tear them back down on Sunday.

Thanks.. Gary

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Setting Zenith Float Height-zenith-float-valve.jpg  
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Last edited by glmoore0001; 11-17-2022 at 06:24 AM. Reason: adding information
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  #2  
Old 11-17-2022, 11:26 AM
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Float adjustment procedure.
Pages 8-9: Float Level

pg 34:

Float (mm)
18-20

21-23 with Solid Needle pin / 18-21 with spring-ball needle pin



Also do a complete setup in the order specified in the rest of the manual.
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Old 11-17-2022, 04:26 PM
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Thank you sir..

I am unsure which style float needle I have. Can you tell me which style is pictured in the attachment?

The pins goes up and down freely, does not feel like there is a spring in there, so I am guessing solid pin.
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  #4  
Old 11-19-2022, 08:42 PM
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yes to solid pin based on that photo.

If you've cleaned it enough you can put it your lips and blow on it. With that pin pulled down (out) from gravity, air should flow through. With it pushed up by the float (in), it should block air.

One thing I learned over the years with zeniths is to watch part of the tuning instructions where they say to close off that little vent port of the top and make sure that when you close of either one, you get the same DROP in rpms.

Every now and then I found a carb when the rpms went UP when you closed that port and that always meant something was clogged up in the middle or lower sections of the castings.

BTW, to close that little port, the ideal tool is a pencil eraser. Those #2 pencils are still good for something.

-CTH
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Old 11-21-2022, 12:37 PM
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Do the vent ports appear to have screens in the bottom? I made sure they were clean when I last had it apart, but I had no idea of their purpose.
The fuel return valve is new, purchased out of Germay.
Thank you for the good info CTH.
After looking at my new float valves, I am pretty sure the valves which now reside in the carbs are trash.
Temps here in Northern Illinois have been below freezing since I last tried to drive the car . If it warms a bit, I will be back at it.
Thanks.. Gary Moore
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  #6  
Old 11-25-2022, 02:39 PM
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>> Temps here in Northern Illinois have been below freezing since I last tried to drive the car .
You will want to make sure that the heat riser flaps are functional (can move).

Where the exhaust meets the intake, there's a thick insulator. Just below that should be a shaft running fore-aft in each of the ports. On one end of the shaft should be a spring. On the other end, a weight. you should be able to spin the weight a little. The spring resistance will be noticeable. If the weight won't budge, the next question is if the flap inside the manifold is pointing up (open) or horizonal (closed).

Closed is a lot better than open, since it means the it takes longer for the exhaust gas to warm the intake. Stuck open means the exhaust is always warming the intake and getting it too hot after a while.

If it's stuck closed in the summer, you won't care. If it's stuck closed in the winter, the car will be less happy during warm up.

-CTH
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Old 11-30-2022, 01:53 PM
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Thank you very much CTH. That is another piece of info I didn't have. Gary

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