Ditched the "Air Maze"...

[old ugly]

have you ever seen a Model A flood and soak the filter and when the engine baack fires, you now have a fire that you would not have if not for the air maze filter

No i have not.
How many cars has that actually happened to?
in all my years i have never seen one catch fire. i have seen lots of leaky model A carbs. most are on cars that an un-mechanically inclined person has tinkered with and they should not have. And it was usually tinkered with after watching youtube

That sounds to me like a maintenance issue not a carburetor's fault. if that carb was set up properly, functioning properly and the fuel system clean it would not leak. Why would the car back fire through the carb from too much fuel (ignition issue but not too much fuel) and if it did happen then that air filter would have to be made of paper not metal screen.
Problem is there is so much bla bla bal out there on how to rebuild a Model A carb, test for leaks and set the float level. Most of them have no idea how to and what is correct.

take the time to find out why that carb drips and fix it properly or take it to someone that can.

have you heard this. sunday morning comes and we are in a hurry to get to the car show, carb has a leak and is dripping on the floor. ooh well i will look at it when i get back home. next sunday comes. oh i forgot to look at that leak ooh well i will look at it when i get home. we have all put things off because we are in a rush.

 

[RENNERS CORNER]

If we look at a Stromberg 97, the float bowl is vented to the atmosphere and were ran with air filters... so is the difference in the jetting?

The 97 was internally vented as far as I know.

This is also something you can't fix with jetting because restriction due to an air cleaner being plugged up changes the dirtier it get, so you cannot fix this with carburetor jetting because jetting is static.

 

[Lawrie]

I have looked at the B 2 carb on my bench, It would be fairly easy to alter the bowl air vent to a balanced style.(air cleaner is fitted)
My thoughts are to block it off at position U and drill a connecting hole through to the idle air supply that is connected to the carb just under the Venturi.
my question is, would it matter that when the choke is on it will be above the choke butterfly, should it be between the choke butterfly and the air cleaner.
Lawrie

 

[RENNERS CORNER]

ALL Ford released Model A & B Tillotson and Marvel carburetors have externally vented float bowls. ALL carburetors that have an air filter have the float bowl internally vented. Those are the two different styles, externally vented and internally vented. I know that you all have pulled an air cleaner off of a more modern carburetor and seen that brass tube coming up on an angle near the choke plate. That is the float bowl vent, with some it is just an internal pathway.


When you put a restriction of any type over the inlet of a carburetor, engine vacuum pulls air through the external float bowl vent, accelerating the fuel through the Jets. This is what causes the rich condition. The amount of fuel accelerated through the jets changes with how much the restriction is at the choke airhorn so as your filter gets dirtier, the rich condition gets worse, this is not something that you might even feel or notice, it is very slight, and that extra unregulated fuel going through the engine over time accelerates wear by washing off oil from the cylinder walls.

Carburetors that have the float bowl internally vented do not have an external vent hole for air. All of the air that goes into the engine must pass through the choke horn area.

No one would think about driving around with their choke partly on, but they'll think nothing of putting on a device that causes a similar condition.
This is not something you will notice by taking the filter on and off. This is so subtle that precise measuring devices like a flow bench has to be used to measure it, but that doesn't mean it's not doing harm.


This is not just something that's being made up. This is carburetor design 101.

Zenith even put out a publication warning people to not put things in front of the carburetor intake that has the float bowl external vented.

Zenith was not ever telling you not to use an air cleaner just not on that specific design of carburetor with an external float bowl vent.

Anyway, all I can do is try and help people understand this and learn.

Like I said earlier, no one is going to argue that filters aren't a good idea but you can't put them on something that wasn't designed for them without the possibility of it causing damage.

 

[RENNERS CORNER]

I have looked at the B 2 carb on my bench, It would be fairly easy to alter the bowl air vent to a balanced style.(air cleaner is fitted)
My thoughts are to block it off at position U and drill a connecting hole through to the idle air supply that is connected to the carb just under the Venturi.
my question is, would it matter that when the choke is on it will be above the choke butterfly, should it be between the choke butterfly and the air cleaner.
Lawrie

No need to reinvent pressure balancing a model B carburetor. I have already written instructions on how to do this.
Just send me an email requesting the information. david@rennerscorner.com

In this application it doesn't matter if it's before or after the choke plate because the choke is not on other than very momentarily.

Vehicles where the choke is on for extended periods, this would be important because it would pull a vacuum on the internal float bowl vent if located below the choke plate.

 

[nkaminar]

The older style carburetors were designed to use gravity feed, especially the Model T where the level in the tank is just a few inches above the carburetor inlet. I am wondering if the lower pressure in the float bowl in a modified older carburetor (Zenith) would effect fuel flow and the level of fuel in the float bowl. More modern carburetor were designed to use fuel pumps were the pressure into the carburetor is greater.

Added: The reduced pressure in the float bowl will have the effect of increasing the fuel pressure into the carburetor from gravity feed. I know running on a fuel pump the pressure out of the pump has to be reduced to use it on an old style carburetor.

 

[Bruce of MN]

On the other hand, it seems like the pump output pressure has to be matched to what the float valve can resist.

 

[Y-Blockhead]

I was running a K&N E-9257 filter on my Marvel but then I went to a air scoop for more performance... haha. Joking, I can see no difference.

 

[Y-Blockhead]

The 97 was internally vented as far as I know.

This is also something you can't fix with jetting because restriction due to an air cleaner being plugged up changes the dirtier it get, so you cannot fix this with carburetor jetting because jetting is static.

The Stromberg 97 is open to the atmosphere thru the orifice where the accelerator pump passes thru??

 

[Bigsnapper43]

Some where in my past of collecting I ran across a service manual issued to mechanics during the Big war in 1940 that had a complete section on the Zenith carbs used by the government. There was much paper used telling the wrenches to not put an air filter on the Zenith carbs that looked like our Z's.

 

[Flathead]

The Stromberg 97 is open to the atmosphere thru the orifice where the accelerator pump passes thru??

Yes, I was looking at one recently and that is what I saw, 97's were used with mesh style rudimentary air cleaners. I have my own opinions but this is getting confusing. There may never be any consensus, kind of like what motor oil to use.

 

[RENNERS CORNER]

Yes, I was looking at one recently and that is what I saw, 97's were used with mesh style rudimentary air cleaners. I have my own opinions but this is getting confusing. There may never be any consensus, kind of like what motor oil to use.

That just it... people are always wanting to bring in opinion when this is science and facts.

Opinions are worthless... like arguing green cars are better than blue cars....

Most of the early air cleaners where mesh and oil bath which don't plug up or cause restriction when dirty.

The oil debate is often a click bait, pot stir tactic used to get people riled.

In the end its pointless because the end failure is no oil in the engine that it fails not what type etc...

 

[RENNERS CORNER]

Some where in my past of collecting I ran across a service manual issued to mechanics during the Big war in 1940 that had a complete section on the Zenith carbs used by the government. There was much paper used telling the wrenches to not put an air filter on the Zenith carbs that looked like our Z's.

That would be interesting if you could find that manual again and post it.

Back when there were 2 types of carburetors being used by manufactures this would have been common knowledge, today we only know the carburetor design type that uses an air cleaner.

 

[RENNERS CORNER]

The Stromberg 97 is open to the atmosphere thru the orifice where the accelerator pump passes thru??

I see the area your talking about, Its been a while since I've studied one of them... what keeps dirt water etc. from entering that area if its open to the bowl ?

Seems like I remember its only an opening when the accelerator pump is active??

I'll have to dig one out and investigate more.

Back when these carburetors were used in production most of the air cleaners were only mesh or oil bath which won't cause a restriction due to their design. Pot of oil with air moving by... so these designs weren't causing issues.
Same reason the Model B Zenith could use the oil bath in 1932 without moving the float bowl vent.

 

[RENNERS CORNER]

I was running a K&N E-9257 filter on my Marvel but then I went to a air scoop for more performance... haha. Joking, I can see no difference.

Interesting scoop keeps the carburetor from pulling heat and leaking exhaust gasses.

I have found using my Superflow bench test equipment that the Air Maze elbow with out an element just the aluminum elbow facing down it the best, it actually increases the cfm thru the carburetor but as you roll the elbow sideways and then facing up the flow was the worst.

 

[nkaminar]

I am going to guess that with the elbow facing down the airflow is set up to turn up through the venturi. With the elbow up or sideways that is not the case. Air flow can be funny through a series of turns. That is why a generous radius is used when the lowest pressure loss is desired. CAD programs like Solidworks have options where the flow through a passage can be visualized. The flow is always surprising. For instance, with a straight inlet the flow gets restricted just past the opening. That is why horns are used on the inlet to carburetors on racing cars.

 

[Jeff/Illinois]

Another thought on this subject comes to mind.
Today's road and driving environment are night and day compared to what the Model A's were exposed to when they were new. There were few hard roads most were dirt-mud-gravel. Most A's ran without an AirMaze or any kind of filter and they were just fine.

Maybe we all worry too much Just keep changing the oil regularly. Poured Babbitt is designed to handle grit without damaging the crankshaft.
And a Model A Ford has to be the easiest thing to change oil in, that is out there.

 

[RENNERS CORNER]

I am going to guess that with the elbow facing down the airflow is set up to turn up through the venturi. With the elbow up or sideways that is not the case. Air flow can be funny through a series of turns. That is why a generous radius is used when the lowest pressure loss is desired. CAD programs like Solidworks have options where the flow through a passage can be visualized. The flow is always surprising. For instance, with a straight inlet the flow gets restricted just past the opening. That is why horns are used on the inlet to carburetors on racing cars.

EXACTLY !

That what makes all of this so difficult for most people because things are not as they seem and without precision measuring equipment, people are just guessing and then using their guess work as fact or proof.

The problem is that modifications to an original design can have devastating effects long term. The slightest seemingly unmeasurable bit of raw fuel that is passing through an engine over even very few miles can ruin it.

We wouldn't drive around with our choke on just ever so slightly, but we will drive around with a restrictive filter or plastic piping to a filter that essentially is doing the same thing.

All of these systems were designed and engineered to work together by the best in the world, to think we know better today is foolish.

 

[RENNERS CORNER]

Another thought on this subject comes to mind.
Today's road and driving environment are night and day compared to what the Model A's were exposed to when they were new. There were few hard roads most were dirt-mud-gravel. Most A's ran without an AirMaze or any kind of filter and they were just fine.

Maybe we all worry too much Just keep changing the oil regularly. Poured Babbitt is designed to handle grit without damaging the crankshaft.
And a Model A Ford has to be the easiest thing to change oil in, that is out there.

I think your right, people worrying about a problem that doesn't exist.

I've yet to see a worn out model A today, all the 90 year old engines yes but today putting maybe 2000 miles a year on most engines... the will last for ever even if they were in the desert.

Running a restrictive filter causing trace amounts of raw fuel to pass thru the engine could however cause premature wear worse than any dust.

Knowledge is key, like they say !

 

[Y-Blockhead]

Interesting scoop keeps the carburetor from pulling heat and leaking exhaust gasses.

David, That was my exact intention. I was just joking about the higher performance, haha.