Air-balancing a Zenith Carburetor

Conaway2

Conaway2

Well-known member
What’s involved in doing this ? I run a high-boy K&N air filter, but am willing to try air-balancing if it’s not too involved.

Thanks- JIm
 
The Model A clone carbs that I have seen used on Gleaner combines and other applications that required a better air cleaner, used something like the one shown in the link above that I posted, with the tube running from the bowl vent to just in front of the choke as part of the casting.
 
30 Closed Cab PU said:
Berts can balance your carb, but you have to pay for it. They add a plug to carb bowl air vent, and machine a passage from the carb bowl to venturi, machine a passage
https://www.santaanitaas.org/wp-content/uploads/2018/08/Modified-Zenith.pdf


A link to the modification, a Tom Endy article. If you are handy can do this yourself.
Click to expand...

Yes, I have one similar to this. The vent is blocked off on the side and rerouted to the carb throat. It does NOT have to be routed in front of the choke plate.

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The one on my Town Sedan now was done by Renner's Corner (Renner's refers to it as "Pressure Balanced"). https://rennerscorner.com/carburetor-services.html It also has Renner's 'Flowed' Jet Set. Runs real good.
 
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Thanks all for your comments - sounds like it’s worth doing. I’m going to make the modifications myself - will report back when complete.

Thanks - Jim
 
I did the machine work on my Zenith-2 carb lower half this afternoon, (followed the Santa Anita A’s article to the letter) and was very disappointed with the results. I machined a groove in a repro Venturi and used flow-tested jets from Renner’s Corner. The engine idled great - better than before, and had lots of power at 40+ mph. However, acceleration from idle to higher speeds was hesitant and stumbling. Another local club member has reported a similar experience to me.

I undertook this project as I am running a high-boy K&N air filter, and have had no issues at all. After reading all the posts about the need for air-balancing the carb when using an air filter, not sure I believe it. Tomorrow, my project will be to return the carb to it’s original condition.....unless anyone has insights as to what I might have missed..

Thanks - Jim
 
Conaway2 said:
.....................unless anyone has insights as to what I might have missed..
Thanks - Jim
Click to expand...

I ran my own calculations 12 years ago using the formulas at the K&N web site and 200.5 cubic engine running at 2100 rpm and selected a K&N E-3050. To date I have over 30,000 miles using a K&N E-3050 and have never had any fouling of my spark plugs.

Here is a link to the same calculation on Model -A.org.
http://www.model-a.org/filtering_air_into_carb.html
"The calculation on the web site are for an engine running 2800 rpm, and they conclude any of the three filters below are adequately sized.
◦K&N offers several filters that can be used with the Air Maze housing.
◾Part # E-3050 is 3.5 inches long.
◾Part # E-9257 is 5.5 inches long.
◾Part # E-2040 is 6.625 inches long.
But the site make this recommendation.
“◦To provide some margin for the filter getting dirty, before you get around to cleaning it, they recommend the 5.5 inch long length. They know it is an over kill, but they are currently using the 6.625 inch long one to allow for driving on dusty gravel roads and to extend their time between filter cleaning / re-oiling cycles.”


I agree that if you put an air filter on a vehicle that is not rated at the CFM per minute of air flow that the engine requires to run at performance RPM you will have an engine that runs rich and fouls plugs. The paper filters that are offered by some vendors to fit the air maze filter housing do not have any CFM rating, they just happen to be the right physical size, and they will restrict air flow and result in fouled spark plugs!!
 
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I am currently running a standard zenith with flow tested jets - do not have the balancing mod.. Have a rebuilt motor/3.54 rear end/no Mitchel. Gas mileage about 15 mpg, plug condition OK.

I have also tried the high boy with the 3050 K and N, did notice the idle changed slightly down (50 RPM or so) so assume there is a slight restriction in air flow, but plug condition, power, and mileage stayed the same with the filter on or off. This year am going to try the High boy with the 9257 filter. Currently do not have the filter on. I do recommend you tether the high boy to the car in case the high boy vibrates off the carb. I tethered mine to a radiator support rod. Also make sure the gas seep hole in the bottom of the air intake does not get blocked, I trimmed a small minimal "V" in the high boy connection hose to insure the seep hole was not blocked. Make sure you really tighten down the hose clamp using a socket and ratchet, I could not get mine to tighten sufficiently using a flat blade screwdriver.. Also by V ing it I was able to get it to seat further onto the carb, and have not had it fall off since.

The air balancing mod has strong opinions on both sides, needing it vs not needing it. Some say if you use an air filter with good flow like the K and N the mod is not needed. Others say not to use an air filter since an air filter messes up the carburation no matter what type of filter is used.

I do not know what to believe. So I personally may try modifying my spare carb with a Dremel, blocking the bowl vent, and drill the hole to the air intake. If things go south I will find a used or purchase a lower carb assy., and transfer the parts from the old one.
I classify this subject with "whats the best oil" debate, strong opinions. Try things, make up your mind what you are comfortable with and what works for you. It's part of the fun of the hobby.
I prefer to run with an air filter. As I said above many say it is not needed. - Personal preference.
 
I was able to return my carburetor to it’s pre-mod performance by removing the brass plug in the bowl vent hole and replacing the modified Venturi with the original one, which blocks the extra hole I had drilled. The channel I machined above the secondary well is still there, but does not appear to affect performance.

I satisfied my curiosity, and didn’t ruin a good carburetor lower half.
 
30 Closed Cab PU said:
Berts can balance your carb, but you have to pay for it. They add a plug to carb bowl air vent, and machine a passage from the carb bowl to venturi, machine a passage
https://www.santaanitaas.org/wp-content/uploads/2018/08/Modified-Zenith.pdf


A link to the modification, a Tom Endy article. If you are handy can do this yourself.
Click to expand...

This is very strange..... Berts doesn't add pressure balancing circuits to carburetors. Another strange thing is that this carburetor in Tom's article looks suspiciously like one that I did. The article talks about theory and pressure differences etc.... that is really not correct, it's really not that complicated. Basically it's just relocating the flow bowl vent. Originally ALL the Ford Model A & B released carburetors had the float bowl vented externally. All carburetors designed to use an air cleaners have the float bowl vented internally that way as the filter gets dirty the restriction can't cause extra air to be pulled thru the external vent and push extra fuel thru the jets causing a rich condition. When the float bowl is vented internally and the air filter gets plugged up, everything is restricted all air and fuel. There is no back door to get extra unregulated dair and fuel into the carburetor.
 
30 Closed Cab PU said:
Berts can balance your carb, but you have to pay for it. They add a plug to carb bowl air vent, and machine a passage from the carb bowl to venturi, machine a passage
https://www.santaanitaas.org/wp-content/uploads/2018/08/Modified-Zenith.pdf


A link to the modification, a Tom Endy article. If you are handy can do this yourself.
Click to expand...

This is very strange..... Berts doesn't add pressure balancing circuits to carburetors. Another strange thing is that this carburetor in Tom's article looks suspiciously like one that I did. The article talks about theory and pressure differences etc.... that is really not correct, it's really not that complicated. Basically it's just relocating the flow bowl vent. Originally ALL the Ford Model A & B released carburetors had the float bowl vented externally. All carburetors designed to use an air cleaners have the float bowl vented internally that way as the filter gets dirty the restriction can't cause extra air to be pulled thru the external vent and push extra fuel thru the jets causing a rich condition. When the float bowl is vented internally and the air filter gets plugged up, everything is restricted all air and fuel. There is no back door to get extra unregulated air and fuel into the carburetor.
 
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There is no "opinion" about the air balancing modification and air cleaner use.

You either understand carburetor theory or you don't......
 
There is an other venturi modification method I have seen.

It is an aluminum repro venturi with a "rounded" groove cut in the venturi instead of the square groove shown in the Endy article.
 
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