Fuel level / Pressure effects on engine operation

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Fuel level / Pressure effects on engine operation

Post by Novice » Sun Sep 29, 2019 12:49 am

My open express has a 9 gallon oval tank under the front seat. I started it up today and ran it for about 5 minutes before it died. while it was running it ran somewhat rough and didn't want to run on magneto and was popping back a little and I couldn't find the sweet spot with spark and gas. switched back to battery engine still running rough Then after a few minutes the engine died and wouldnt restart. But would try to start with the choke pulled. I checked the gas in the tank with the measuring stick and it showed about half a inch in the tank. (Out of Gas) My question is what effect if any have others observed with a full,half,quarter. almost empty under seat tank cars. How much effect does fuel pressure have on a model T. would a fuel pump make for more power and a smoother running engine with different levels of gas in the tank.
or just keep it half full and dont worry about it.


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Re: Fuel level / Pressure effects on engine operation

Post by Joe Reid » Sun Sep 29, 2019 1:02 am

How does your fuel line run from the bulb? Is it level? You are low on gas and keeping the tank fuller would help. How much gas do you usually keep in it? Does it run ok when it is fuller? I would never consider using a fuel pump, make sure your fuel line is routed correctly and keep gas in it. I have tractors and cars and they always sputter when they get low. Air leaks can also cause problems, make sure the carb gasket is good and also intake manifold.

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Re: Fuel level / Pressure effects on engine operation

Post by Doug Keppler » Sun Sep 29, 2019 7:43 am

Jim, I have the same, oval tank under the seat. A couple of weeks ago I checked my fuel level, had 4 gallons of gas and went out for a ride with the family. We got to a moderately steep hill on the back roads, the car sputtered and died and would not start. I rolled backwards down the hill into a level driveway and it started right up. So I have to have at least 3/4 tank of gas in order to pull hills, well Im not going to stand for that I want to drive my car. I wont say how I solved the problem here on the forum for fear of being burned at the stake but I no longer need to worry about having enough gas to go up a hill anymore
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Re: Fuel level / Pressure effects on engine operation

Post by Henry K. Lee » Sun Sep 29, 2019 7:48 am

Magical Pixie dust in the fuel tank?

Hank

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Re: Fuel level / Pressure effects on engine operation

Post by Doug Keppler » Sun Sep 29, 2019 7:56 am

Hank Knows because he is a purveyor of magical pixie dust
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Re: Fuel level / Pressure effects on engine operation

Post by Humblej » Sun Sep 29, 2019 8:07 am

Jim, just keep it above half and dont worry about it.


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Re: Fuel level / Pressure effects on engine operation

Post by DickC » Sun Sep 29, 2019 9:01 am

We wrote about this several weeks ago. The amount of gas in the tank is often the cause of vapor lock also. Because the fuel line passes the exhaust so closely, the fuel pressure of less than a full tank will cause the fuel line to vapor lock. Sometimes on a hot day and running a little hard, I have had vapor lock with 1/2 tank. Fill the tank and it runs fine.


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Re: Fuel level / Pressure effects on engine operation

Post by Henry K. Lee » Sun Sep 29, 2019 9:35 am

Vapor Lock? That happens to my bride all the time, fill her back up with more beer and wine and she works just fine too.

Sometimes she amids I am right! Keep em topped off folks!

Hank


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Re: Fuel level / Pressure effects on engine operation

Post by Henry K. Lee » Sun Sep 29, 2019 9:37 am

Oh and by the way, high octane grain alcohol makes them spit and spudder for what it is worth both car and wife!


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Re: Fuel level / Pressure effects on engine operation

Post by Henry K. Lee » Sun Sep 29, 2019 9:38 am

And hard to restart in the morning after!

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Re: Fuel level / Pressure effects on engine operation

Post by Steve Jelf » Sun Sep 29, 2019 10:29 am

There's a saying that with a Model T two gallons is plenty and one gallon is not enough. I always carry extra gas on the running board, so if I get down to the sputtering point I put in two or three more gallons and refill the can at the next filling station.

IMG_1740 copy.JPG
Some people will hate this, but I avoid vapor lock by running the fuel line under the exhaust pipe. As you can see, there's a lot of space between them.
The inevitable often happens.
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Re: Fuel level / Pressure effects on engine operation

Post by Hal » Sun Sep 29, 2019 10:51 am

I don't live in the mountains. But that is not to say we don't have any hills, because we do. I have never experienced any rough running I could attribute to low fuel except for the 3 or 4 times I have actually run out. My TT has the oval tank and her Touring has the round one. I typically buy gas when I'm below say 2" on either.

None of this is to say I don't believe others when they say they have these problems. But it never ceases to amaze me at the differences between these cars that are otherwise so similar to each other.

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Re: Fuel level / Pressure effects on engine operation

Post by Oldav8tor » Tue Oct 01, 2019 9:57 pm

I just got back from the Covered Bridge tour in Indiana. Plenty of steep hills on the tour routes. One time going up a steep narrow dirt road my car acted like it was going to die a few times. We made it to the top (thankfully) and filled the tank about 5 miles later. I put a little over 5 gallons into the 10 gallon round tank under my seat.

I cringe to think of what I would have done if it had died. The road was too narrow to turn around and was not straight. Rolling backwards with nothing but my ineffectual transmission brake might not have had a good outcome, especially for the car coming up behind me. Pixie dust sounds like a good safety item. Some details please :D
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Re: Fuel level / Pressure effects on engine operation

Post by Loftfield » Wed Oct 02, 2019 8:07 am

Here in the Southern Highlands of North Carolina we measure the gradient of roads in gallons. We yet do not have any definitive empirical data on just how steep a hill is required for any particular gallon designation, all more or less by guess and by golly. In my 1912 I have to have three gallons in the tank to get up the hill on US 64 between home and the farm (a three-gallon hill), seven gallons to get up my driveway (a seven-gallon hill), etc. Of course, if caught short one can always back up the hill. At least half the fun of antique cars is engaging in living history. I have removed electric fuel pumps that came on cars I have purchased. If you aren't willing to keep abreast of the amount of fuel in your tank then maybe you should have something other than a Model T.

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another thought

Post by Dropacent » Wed Oct 02, 2019 4:06 pm

Just going to throw this out here. Recently I got an engine of the same era running. 1909 . Primitive carb, like the primitive carbs on the T. Ran fine, until I started up the driveway, where it would spit sputter and stall. Sitting still it would run fine, rev up, etc. I dug into the early original literature of this Schebler carb. What caught my eye was they stated IT WAS VERY IMPORTANT to not have too small of a gas line. The internal dimension is what is important. I believe they stated 3/16” was the minimum ID. It’s possible to use brake line or similar that appears to be the right size, but in fact, the ID is too small. That little change made all the difference in the world, and took care of all my stumbling issues. Sometimes it is the simplest solution to a hair pulling problem.

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Re: Fuel level / Pressure effects on engine operation

Post by Oldav8tor » Wed Oct 02, 2019 9:56 pm

Thomas,
"If you aren't willing to keep abreast of the amount of fuel in your tank then maybe you should have something other than a Model T."

I just came off the Covered Bridges Tour in Indiana. My "stumbling" incident occurred before we had come upon the first gas station on the published route. In the future I may carry an extra gas can for such situations, but there was no warning about the steepness of the hill and in any case, I thought 5 gallons should be plenty for whatever hills we came across. I'm new to Model T's and had never experienced such a thing before.

As a pilot for the past 44 years, I am very aware of how much fuel is in my tanks, car, plane or boat. The latter two have a very embarrassing scenario if you run out of fuel. Fortunately, I didn't have to learn that the hard way :D
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Re: Fuel level / Pressure effects on engine operation

Post by Russ T Fender » Thu Oct 03, 2019 12:50 pm

Years ago I bought a T that had been sitting for years. I offered one price if I could hear it running and it sounded OK and a considerably lower price if it was not running. They agreed and spent 2 hours trying to get it to run before they finally agreed to accept the lower price. I loaded the car on to my trailer and left. I stopped for gas in my tow vehicle on the way home and decided to stick the tank in the T as well. There was about 1 gallon of gas in the tank. I filled it up and went home. On a lark I tried to start the T rather than winch it off the trailer. It started on the first pull and has been running ever since! Bottom line, you need at least 2 gallons, maybe even 3, in the tank to ensure starting. I have encountered that problem in other early cars as well. They might start after choking but quickly die once the gas in the carburetor is exhausted. The simple fix is more gas in the tank!


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Re: Fuel level / Pressure effects on engine operation

Post by Scott_Conger » Thu Oct 03, 2019 4:51 pm

It is all about Cv, or flow coefficient of your fuel system. Are you draining your tank through a fire hose or a syringe needle? They both have atmospheric pressure at the tank, but one will clearly starve the car of fuel. If you cannot guess which one, stop reading now.

Not all carburetors have the same Cv through the float valve from one brand to another, and even within the same brand/model of carb. Put 3 NH carbs on a table...look hard at them, and I'll bet you that one of them will cause a car to view that steep hill as an 8 gallon hill, and another carb will take the hill with 4 gallons, and with ease. Without a fuel pump.

And now, for the final hint: The shiny new float valve you bought from your favorite supplier for your NH, is almost with certainty, not made to flow fuel properly.
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Full Flow Float Valves - deliver fuel like Henry intended!

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