Gasoline/Petrol vs BTU's

G

Growley bear

Well-known member
A few (3?) years ago It was mentioned that installing a Model B cyl. head would be something that I might like.
I installed model b head-camshaft-distributor-already had b intake manifold. Engine bored to .100 OS and a good Zenith carburetor. I liked the extra hill climbing ability and the 3.54 gears seemed more like stock Model A. All was well until I became the proud owner of a couple of very rusty Zenith B1-2 carburetors, one of each. The first order of business was to find out and learn everything that I could about the B carbs. Not much different than the A, but different enough. I also have 3 different charts for comparison.
Now to flow test the jets. I found that the flow charts seemed a little on the lean side, but persisted, especially w/idle jet. I also ended up with a bit larger comp and main jet. This has turned out to be a very wise choice at least for me.
I was puzzled though as to why the jets needed to flow so much more fuel. I think I have the answer.
Not knowing when the charts were made, I can only guess that the gasoline/petrol has been laced with more alcohol there by diluting the BTU count per pound of fuel. I use a 36 inch head of water per Tom Endys' paper on flow testing jets.
Has anyone had similar experiences and maybe some thoughts in this area. I think that this would be helpful information for anyone not too familiar with the process as much patience is required here. I want to express my thanks to the folks who have taken the time to draw up these flow charts as I know it wasn't easy.
The engine purrs along and pulls very strong, so to pass it on, if you have been thinking about a B conversion on an A engine, try it you'll like it.
 
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Today's gasoline is leaner because of the alcohol content. Original jet sizes are for "real" gasoline.
 
I don't know if his relates or not. I bought a 641 Ford tractor to mow with. It struggled to pull a 6' mower. It had a fixed jet Zenith carburetor. I increased the jet size 8%. Made a great improvement. I should have gone 10%. Still runs a bit lean.
 
I just bought a set of flow tested jets for a Zenith 3 from Renner's corner. I wonder whether they were tested for E10 or "proper" fuel. In ever use ethanol fuel so if they were tested for the fuel available over there, I'd be running rich I didn't consider that when I ordered them.
Anybody know? I could always email Renner's and ask I suppose.
 
I ordered a set of jets from Renner's about three years ago for my Zenith 1 and they worked perfectly. They are on top of their game at Renner's.
I just like to adjust my own as it is a fun, and educational, challenge.
 
Guess you would have to know the % of differences of flow thru a given orifice between the different fuels to calculate the flow rate. Different parts of the country have different fuels, different altitudes etc, it would be hard for someone to flow them but to a general average. :)
Oh! In case someone is wondering, the jets are flow tested with water, not fuel.
 
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In southern NH the gas has different blends between the summer and winter because our supply comes from Massachusetts. It has something to do with emissions.
I do a lot of driving and can see a 1-2 mpg difference in my modern car.
I guess this would also make a difference in my A and T.
 
estout81 said:
I don't know if his relates or not. I bought a 641 Ford tractor to mow with. It struggled to pull a 6' mower. It had a fixed jet Zenith carburetor. I increased the jet size 8%. Made a great improvement. I should have gone 10%. Still runs a bit lean.
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Yes, I think it relates very closely. I calculated the following increased flow rates w/water at 100ft. MSL for my B2 carburetor w/36 inch head pressure following the chart published in Restoring "A" & "B" Carburetors The Rex Reheis Way.

1) Main---no increase needed from recommended

2) Cap----no increase needed from recommended

3) Compensator---13% increased flow

4) Idle---48% increased flow

5) Power---1.2% increased flow

The comp needed an increase to allow for running with the GAV open 1/2 turn vs. 2 turns. And when closed just a faint difference in idle quality can be detected.
The idle was gradually opened just enough to allow for a smooth easy idle @ 1/2 turn open of the idle air screw.

I have no real idea of the amount of time involved in this jet tuning adventure and it is far from over.
 
nhusa said:
In southern NH the gas has different blends between the summer and winter because our supply comes from Massachusetts. It has something to do with emissions.
I do a lot of driving and can see a 1-2 mpg difference in my modern car.
I guess this would also make a difference in my A and T.
Click to expand...

I think it would be interesting to know if published figures exist concerning the fuel quality '30s--'50s through to unleaded and the junk corn fed fuel we have now. I have read statements from Ford that 25 mpg was possible but there was no mention at the speed of the vehicle and or engine. I believe that the numbers were recorded at no more than 35 mph considering the road quality mostly in those days.
My experience says that when a person drives a Model A; don't be in a hurry and don't be too concerned with fuel economy as long as the engine is running well.
 
I have a 1000 mile average of 23 mpg with speeds over 55, much of it at 65(stock rear, no overdrive)
never tested the flow of the jets, but did do a loaded emission test before and after ethonal ---no changes to car

regular gas, closed GAV, full advance ---HC ppm 190, CO 4.8% ---this got me 23 mpg

ethonal 10% gas ---closed gav, full advance, HC ppm 60, CO 0.15% NOX ppm 853(was good enough to pass as 2000 auto) ---but not driveable on the road
so at 1/4 gav the co came up to 1,5% , (plugs burn near white), driveable, but up near 3000 rpm the gav needed to be nearer to 1/2 to keep 1.5%

I havn't tried to keep track of fuel mileage lately but it is over 20---have put over 100 miles on 10$ gas ---mix of slow parade,local and highway use
 
Kurt in NJ said:
I have a 1000 mile average of 23 mpg with speeds over 55, much of it at 65(stock rear, no overdrive)
never tested the flow of the jets, but did do a loaded emission test before and after ethonal ---no changes to car

regular gas, closed GAV, full advance ---HC ppm 190, CO 4.8% ---this got me 23 mpg

ethonal 10% gas ---closed gav, full advance, HC ppm 60, CO 0.15% NOX ppm 853(was good enough to pass as 2000 auto) ---but not driveable on the road
so at 1/4 gav the co came up to 1,5% , (plugs burn near white), driveable, but up near 3000 rpm the gav needed to be nearer to 1/2 to keep 1.5%

I havn't tried to keep track of fuel mileage lately but it is over 20---have put over 100 miles on 10$ gas ---mix of slow parade,local and highway use
Click to expand...
That is very interesting. Good target numbers. I have another B-2 Zenith carburetor that I am in the process of fine tuning. As soon as I am satisfied with it I will start my mileage checks. I'll keep your numbers for a reference, thanks again for the help.
 
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