Zenith Float Bowl Vent Variations

[Thodge]

Does anyone know where I can find some information on the different iterations of Zenith float bowls? More specifically, the changes they made to the vent. I was reading an article somewhere recently about it but can’t seem to find it anywhere now. Is there anything in the service bulletins? I have what I figure to be a late ‘28 model that is not labeled 1,2,or 3 and has no vent hole. Whatever I was reading mentioned something about increasing the size of the vent hole in the earlier vented bowls. I would think the same vent could be added to the bowl I have. I’m questioning the operation of my float with no vent. It’s a pain to get the bowl to fill and the car to run right at first every time you start it after carburetor reassembly.

 

[Jim/GA]

Look in the vicinity of where these arrows point. You should find a vent hole there about 1/8" diameter (maybe a bit smaller, doing it from memory). That's the vent from the bowl in the upper body casting.

Then in the lower body casting, you see 3 holes in a row. The one by the vent from the bowl is the well, the center hole is for the bolt that holds the carb together, and the 3rd hole is the vent. It vents this center passage in the upper carb body where the first hole goes to out to the outside.

Additional holes were added later by Zenith and the 3rd hole was made larger. I don't think you need to. I think Zenith were over compensating.

 

[Thodge]

Thanks for the help. The strange thing with this carb is that there seems to be a small vent passage just behind the idle jet that goes into the float chamber and that’s the only one I found. Admittedly, the upper casting was still on the car and I was looking with a mirror. I blew compressed air through the passage and it came out in the float chamber so I know it’s open. Still every single time you try to start the car after putting the carb together, the float refuses to fill the bowl without some fiddling. Once the bowl finally fills up everything is fine. The tank cap is venting so that’s not the problem.

 

[CT Jack]

You might have a marginal flowrate. Check the the flow going into the carb also try installing another float valve. If you have an inline after market filter this might be restricting the flow. It sounds like you might be shutting your fuel valve and running the carb dry before shutting off your engine. If so, try shutting off the ignition first and then shutting the gas valve. The carb should be full for the next start up.

 

[johnbuckley]

"Does anyone know where I can find some information on the different iterations of Zenith float bowls? More specifically, the changes they made to the vent." Steve Pargeter's excellent booklet "Zenith Model A Craburetor Restoation Guidelines, vers 7a" . from which these diagrams are taken

 

[Thodge]

You might have a marginal flowrate. Check the the flow going into the carb also try installing another float valve. If you have an inline after market filter this might be restricting the flow. It sounds like you might be shutting your fuel valve and running the carb dry before shutting off your engine. If so, try shutting off the ignition first and then shutting the gas valve. The carb should be full for the next start up.

I’ve been wondering about the flow rate too. It seems to fill the sediment bowl quickly when that’s emptied so I’m not sure. It had done it with two different float valves though. The car had an inline filter that I got rid of with a new line and made sure it wasn’t installed too far into the carb. I do wonder if there is rust restricting the tank valve, which is due for replacement as soon as the tank is run down closer to empty. The valve has been leaking slowly so I can’t test whether running the carb dry has the same effect as disassembling the carb because it keeps refilling the bowl overnight.

 

[Thodge]

"Does anyone know where I can find some information on the different iterations of Zenith float bowls? More specifically, the changes they made to the vent." Steve Pargeter's excellent booklet "Zenith Model A Craburetor Restoation Guidelines, vers 7a" . from which these digrams are taken

Thank you. This is exactly the information I was looking for. I’m confused by some of the information in the diagrams though. It was my understanding that the only carbs without the brass secondary wells were early double Venturi carbs. The diagram shows the first use of the secondary well to be mid-29. But isn’t that when they changed over to the machined vs brass GAV seat? My carb has a brass secondary well and GAV seat, which I thought put it mid-28 to mid-29.

 

[johnbuckley]

Still every single time you try to start the car after putting the carb together, the float refuses to fill the bowl without some fiddling. two other possible causes to think about ..1. float valve sticking closed .( come across a couple of times esp with viton tipped ones)
and 2. fuel pipe sticking out too far beyond ferrule - this has occurred both at the carb end and the sediment bowl end on As I've seen.

 

[johnbuckley]

From Pargeter.... ( but I'm sure things were used up from the parts bin whatever ! )
Zenith-mnfd zeniths brass GAV seat from 1927 to late 1929
Zenith-mnfd zeniths brass sec insert well from Jul-Dec 1928 onwards
Zenith-mnfd zeniths single venuri from Jul-Dec 1928 onwards
Holley-mnfd zeniths brass GAV seat from 1928 to Jul-Dec 1929
Holley-mnfd zeniths brass sec insert well from Jul-Dec 1928 onwards
Holley-mnfd zeniths single venuri from Jul-Dec 1928 onwards
[PS pm sent]

 

[Bob Bidonde]

Download this slide.

 

[Thodge]

John - Thanks for that information. I guess the diagram was just over-generalized. The problem has been consistent with two different types of float valves. I was careful not to install the fuel line too deep, with the ferrule almost flush with the line.


Bob - That’s the slide I was trying to find! I must have seen it buried in another thread on here. Thank you.

 

[Big hammer]

Thanks for the help. The strange thing with this carb is that there seems to be a small vent passage just behind the idle jet that goes into the float chamber and that’s the only one I found. Admittedly, the upper casting was still on the car and I was looking with a mirror. I blew compressed air through the passage and it came out in the float chamber so I know it’s open. Still every single time you try to start the car after putting the carb together, the float refuses to fill the bowl without some fiddling. Once the bowl finally fills up everything is fine. The tank cap is venting so that’s not the problem.

Most people have problems with the float valve not closing and leaking !

Define FIDDLE WITH !

Once the bowl fills up everything is fine My guess you have an air lock or vapor lock until you get gas to flow ?

When I had a glass sediment filler at the firewall and a cast iron sediment bowl on the carburetor and the normal filter in the carburetor, at times the carburetor wouldn’t fill until I cracked open the line at the carburetor. I now only have the in tank strainer in the shutoff valve and the normal filter in the carburetor and made sure the gas line is headed down hill , no Whoopty Doos

May I suggest once everything is fine …….. Go for a nice drive and enjoy your A and stop the fiddling with when everything is fine !

 

[47topless]

Wow! This post is a great coincidence for me. I just installed a Zenith 2 and I could not get the fuel to flow into the carb. When the line was disconnected at the inline filter, the gas flowed great, but when the line was all together into the carb, the fuel would not flow.
I was able to finally get it to flow by draining the carb. It now flows good. There was defiantly a vapor lock condition present until the carb was drained. Lots to learn about these old Zeniths.
Thanks for the info.
Phil

 

[johnbuckley]

My guess you have an air lock or vapor lock until you get gas to flow. Oh yes good suggestion which reminds me of a couple of years ago using a float valve like the 3rd from left .... It's height created its own vapour lock ! Hopefully explained by attached pics

 

[Russell Reay]

This is indeed a coincidence. I just bought a Zenith core at a swap meet, and disassembled it before ordering rebuild parts. Mine is the same--or very close-- to Thodge's. To clarify photo #2 (Jim/GA) the vent hole is under the float bracket. This raises the question, with this vent hole, why is it necessary drill a new one as shown in Bob B's excellent slide?

 

[Thodge]

That’s a great suggestion about checking the height of the float valve. I know the repro valve that I just took out was taller than the old one that I put back in. Ford knew they had a problem with the float bowl not venting properly at times or they wouldn’t have changed the vent design. As this carburetor isn’t even correct for the ‘30 car that it’s in, I have no problem adding the extra vent hole that they added in ‘31. Maybe it is overkill, maybe not.

 

[Thodge]

I just now realized when looking at a photo of another float bowl that there’s a piece of the casting on mine missing between the secondary well hole and main bolt hole. Anybody think this is a problem? I wouldn’t think it would make much difference because it seems like it all would be open to the idle air chamber anyhow.

 

[Jim/GA]

I just now realized when looking at a photo of another float bowl that there’s a piece of the casting on mine missing between the secondary well hole and main bolt hole. Anybody think this is a problem? I wouldn’t think it would make much difference because it seems like it all would be open to the idle air chamber anyhow.

Not a problem. If you look in this same area on the upper casting, where it mates to the bottom half, you will see that it is all open and connected across there.

 

[katy]

Define FIDDLE WITH !

https://www.merriam-webster.com/dic...dle (something,had fiddled with the equipment.

 

[Thodge]

I think I’ve reached the point with this particular carburetor that I need a definition on “Fiddled With Oneself”. I think I’m going to move on to a different lower casting altogether.