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05-06-2018, 06:35 AM | #1 |
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Join Date: Apr 2012
Posts: 777
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Gasoline/Petrol vs BTU's
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. Last edited by Growley bear; 05-08-2018 at 07:20 AM. Reason: add text |
05-06-2018, 04:00 PM | #2 |
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Join Date: May 2010
Location: Southern Maine
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Re: Gasoline/Petrol vs BTU's
Today's gasoline is leaner because of the alcohol content. Original jet sizes are for "real" gasoline.
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05-06-2018, 05:15 PM | #3 |
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Join Date: Jun 2010
Location: Utica, Ohio
Posts: 522
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Re: Gasoline/Petrol vs BTU's
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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05-06-2018, 06:11 PM | #4 |
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Join Date: Jun 2014
Location: Melbourne, Australia
Posts: 7,496
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Re: Gasoline/Petrol vs BTU's
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.
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05-07-2018, 06:54 AM | #5 |
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Join Date: Apr 2012
Posts: 777
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Re: Gasoline/Petrol vs BTU's
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. |
05-07-2018, 11:47 AM | #6 |
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Location: Portland OR
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Re: Gasoline/Petrol vs BTU's
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Oh! In case someone is wondering, the jets are flow tested with water, not fuel.
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I know the voices aren't real but damn they have some good ideas! Last edited by redmodelt; 05-07-2018 at 12:24 PM. |
05-07-2018, 03:50 PM | #7 |
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Join Date: Oct 2011
Location: Raleigh, NC
Posts: 549
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Re: Gasoline/Petrol vs BTU's
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. |
05-08-2018, 07:45 AM | #8 | |
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Join Date: Apr 2012
Posts: 777
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Re: Gasoline/Petrol vs BTU's
Quote:
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. |
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05-08-2018, 07:58 AM | #9 | |
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Join Date: Apr 2012
Posts: 777
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Re: Gasoline/Petrol vs BTU's
Quote:
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. |
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05-08-2018, 08:46 PM | #10 |
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Join Date: May 2010
Location: on the Littlefield
Posts: 6,157
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Re: Gasoline/Petrol vs BTU's
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 |
05-09-2018, 06:40 AM | #11 | |
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Re: Gasoline/Petrol vs BTU's
Quote:
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