The Ford Barn

jkeesey · 09-06-2013, 11:19 AM

I was wondering while rebuilding a B carb the other day, has anyone ever done a flow test on the different popular updraft A carbs to see the difference? I have felt the performance differences between them but I would like to see some ink on paper proof.

H. L. Chauvin · 09-06-2013, 11:55 AM

Hi J,

Did not keep the results on paper; but rest assure that for carburetor jets alone, after testing many, flow rates vary from acceptable to unacceptable in both new & original jets.

One way to ruin jets is to enlarge the very tiny openings by using a hard steel wire for cleaning the softer non-ferrous metal -- one can do a better job of ruining jets if the steel wire is rusty, rough, & is shaped like an "L" at the end after cutting the wire with a dull cutting tool.

Others may have better & more detailed carburetor information; but, like your observing same, if one has 3 or 4 carburetors that have different performing jets, there is a noticeable difference in overall performance.

Jim/GA · 09-06-2013, 02:25 PM

What kind of flow test did you have in mind?

How much air will each carb move at Wide Open Throttle (WOT)?

With the larger throttle bore, assuming it is matched with a larger intake runner bore, the Model B carb will win, hands down.

Then you have all the other carbs with the stock throttle plate and bore size. Among them, I think you will find the Marvel-Schebler is the best.

Or were you thinking about the fuel flow characteristics?

jkeesey · 09-06-2013, 03:21 PM

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I like your responses. What I'm interested in is really any statistics. For instance air flow at WOT or say a dyno run similar to the tests they do on modern carburetors. I'm thinking use one known good engine and test several carburetors on it and see what the differences would be.

09-06-2013, 11:19 AM	#1
jkeesey Senior Member Join Date: Apr 2011 Location: Glenmoore Pa Posts: 1,644	Model A Carb comparison I was wondering while rebuilding a B carb the other day, has anyone ever done a flow test on the different popular updraft A carbs to see the difference? I have felt the performance differences between them but I would like to see some ink on paper proof.

09-06-2013, 11:55 AM	#2
H. L. Chauvin Senior Member Join Date: May 2010 Posts: 4,179	Re: Model A Carb comparison Hi J, Did not keep the results on paper; but rest assure that for carburetor jets alone, after testing many, flow rates vary from acceptable to unacceptable in both new & original jets. One way to ruin jets is to enlarge the very tiny openings by using a hard steel wire for cleaning the softer non-ferrous metal -- one can do a better job of ruining jets if the steel wire is rusty, rough, & is shaped like an "L" at the end after cutting the wire with a dull cutting tool. Others may have better & more detailed carburetor information; but, like your observing same, if one has 3 or 4 carburetors that have different performing jets, there is a noticeable difference in overall performance.

09-06-2013, 02:25 PM	#3
Jim/GA Senior Member Join Date: May 2010 Location: Young Harris, GA Posts: 1,821	Re: Model A Carb comparison What kind of flow test did you have in mind? How much air will each carb move at Wide Open Throttle (WOT)? With the larger throttle bore, assuming it is matched with a larger intake runner bore, the Model B carb will win, hands down. Then you have all the other carbs with the stock throttle plate and bore size. Among them, I think you will find the Marvel-Schebler is the best. Or were you thinking about the fuel flow characteristics? __________________ Jim Cannon Former MAFCA Technical Director "Have a Model A day!"

09-06-2013, 03:21 PM	#4
jkeesey Senior Member Join Date: Apr 2011 Location: Glenmoore Pa Posts: 1,644	Re: Model A Carb comparison Sponsored Links (Register now to hide all advertisements) I like your responses. What I'm interested in is really any statistics. For instance air flow at WOT or say a dyno run similar to the tests they do on modern carburetors. I'm thinking use one known good engine and test several carburetors on it and see what the differences would be.