Fuel Lime Diameter

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Model T Ford Forum: Forum 2016: Fuel Lime Diameter
Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Osterman on Tuesday, March 08, 2016 - 10:09 pm:

I have found that as I get to around 40-45 mph my T seems starved for fuel. I installed a carburetor with a wider throttle and intake in the late fall and now that winter is breaking up I'm able to give the car a workout.

Do any of you use 5/16" fuel line? I'm wondering if my 1/16 line is not quite enough to cruse smoothly at 40 mph.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James Baker on Tuesday, March 08, 2016 - 10:13 pm:

They weren't made for that speed. Anyway the fuel line size has nothing to do with it.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Zibell, Huntsville, AL on Tuesday, March 08, 2016 - 10:24 pm:

1/16 inch line is pretty small. Are you sure it is that small? T fuel line is about the same size as steel hydraulic brake line. Check to make sure you don't have any restrictions in the line or sediment bowl. All a larger throat carburetor does is raise the RPM of max efficiency. It doesn't necessarily make a car run better, it fact it can make it worse. The lower air velocity of a larger carburetor doesn't provide as good a mix, so a higher RPM is needed to increase the air speed to get a good mix of the air and fuel. A T engine is a low RPM type of engine.


Top of pagePrevious messageNext messageBottom of page Link to this message  By JD, Wichita, KS on Tuesday, March 08, 2016 - 10:46 pm:

5/16 diameter is about 56% larger area than 1/4.
I don't know if it's necessary, but doesn't hurt.
Especially with gravity feed.
I like copper/nickel brake line.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Tuesday, March 08, 2016 - 10:47 pm:

The steel brake line commonly used for Model T fuel lines has an OD of " and an ID of .180", which is almost 1/5". That's bigger than the opening in a carburetor float valve, so it should be more than enough.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Osterman on Tuesday, March 08, 2016 - 10:48 pm:

Whoops .. I meant I'm currently running 1/4" steel fuel line in my post.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stan Howe Helena, Montana on Tuesday, March 08, 2016 - 10:51 pm:

ALL carburetors work on the compromise dictum: As you gain some things you will lose on others. That's a major reason fuel injection was invented.

That said, a venturi size small enough for good starting and low speed performance may not have enough air flow for higher speeds. Or it may. There are many variables and worlds of different designs.

There were over 200 different accessory carburetors made for the T Ford with varying results. Many of them made had some design to improve higher engine speed performance but to retain low engine speed performance and power.

There are hundreds of variables in carburetor design, a larger venturi with a small main jet or simple orifice instead of a complex orifice/jet design many not run as well as a smaller venturi with a complex orifice/jet design.


The head pressure from a gravity feed tank may or may not be enough to keep the fuel bowl filled to the proper level for performance at higher fuel demand speeds. Most use a 1/4 line, some use a 5/16 line. Generally speaking, if you can use all the fuel a 1/4 line will deliver you are not running a single carburetor T engine.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Osterman on Tuesday, March 08, 2016 - 10:58 pm:

The car runs fine up to around 35 - 40 mph. Actually seems to have faster pick up with the "new" carburetor. Been tweaking the idle and higher speed adjustments trying to dial in the right combination.

I read an earlier discussion about in-line fuel filters having a potential starving effect. Of course I might also need to adjust the float if this is a fuel related issue. It wasn't a problem with the Kingston carburetor I previously had on the car. But that didn't have the pick up I currently haven it's this new carb, which is an advantage when you drive mostly in city traffic as I do on a regular basis.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Tuesday, March 08, 2016 - 11:10 pm:

Yes, if you're using an inline filter that can be a problem. The sediment bulb screen should be enough if the tank is clean.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dick Fischer - Arroyo Grande, CA on Tuesday, March 08, 2016 - 11:10 pm:

Mark,

Here's a simple test to see if your 1/4" fuel line is limiting the top speed of your car:

With the car at top speed and mixture adjusted for best running, try turning the mixture out (richer) a turn or two. Does the car bog down because it's gone too rich ? If so, you have plenty of fuel flow coming through the line. If there's no change when you richen the mixture control, then you are probably flow-limited somewhere else in the supply system. That flow-limiting MIGHT be the fuel line, but it could also be the inlet to the carburetor or an obstruction at the tank or sediment bowl.

Dick


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Osterman on Tuesday, March 08, 2016 - 11:24 pm:

Ha,

I removed the in-line filter tonight and drove around the neighborhood with my feeble lights. Just enough light to keep a look out for pedestrians ... and the cops.

That really seemed to make a big difference. Now I can't remember why I added that filter when I installed the new carburetor. Seemed like a good idea at the time even though I hadn't used one in the past 27 years. Whoops.

Problem solved .... thanks all.

Mark


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