up draft carbs.

F.E.Bear · Feb 9, 2016

Why did most vintage tractors have up-draft carbs?
I started working with tractors 70 plus years ago and I still haven't found out why.

Fred

Sam Womer (PA) · Feb 9, 2016

Probably the main reason is to make it easier to have gravity flow from the gas tank. The elimination of the fuel pump makes it easier to design and build the engine , mount the fuel supply above it and prevent flooding of the engine. Anyone have another WAG?

gene bender · Feb 9, 2016

why put the carb on top then use a fuel pump

centash · Feb 9, 2016

Fuel systems were gravity flow, hence requiring a carb lower than the tank---many old cars were updrafts as well for that reason--think Model T

Ben

Paul Janke · Feb 9, 2016

If the float doesn't shut the needle valve tight and the carburetor is updraft, the gas drips away. If the carburetor is downdraft, the fuel makes its way down into the oil.

Roger in Iowa · Feb 9, 2016

Also kept the hood line lower, in addition to the other mentioned reasons.

David G · Feb 9, 2016

I would vote for gravity flow.

Sprint 6 · Feb 9, 2016

Less prone to flooding the cylinders if over choked. I think updrafts would probably be more economical on fuel usage in a constant speed engine situation such as a tractor. Updraft also reduces perculation issues because the exhaust is above the carb and heat rises. All speculation on my part.

John B. · Feb 9, 2016

I don't think there was a specific reason other than just the way the engines were designed. The Farmall F-12 & F-14 series had a down draft carb and a fuel pump supplied the fuel to them.
I can say that the gas tanks on the F-12 & F-14's were taller in size and by measurement which allowed room under the hood for the carb to sit on top of the engine unlike the styled Farmalls in later years with up draft carbs.
Look at many of the hit and miss engines that relied on vacuum to suck fuel up to the up-draft carbs on many of those engines. Even some of these engines had up draft or down draft carbs.

Athol Carr · Feb 9, 2016

I think that the F-12 etc tractors got downdraft carburetors because the engine designers did not leave enough room to get the spark plugs between the valve push-rods. Hence the spark plugs are on the other side of the engine under the manifold. With the spark plugs there an updraft carburetor was not possible if one needed access to the plugs, so a downdraft carburetor together with fuel pump was fitted. A curse on a gasoline only tractor if the carburetor is dry, it takes quite a bit of cranking to get enough fuel into the carburetor for starting.

old · Feb 9, 2016

Sorry but your wrong on this point. I have seen more then 10 tractor like say an 8N ford with the oil pan full of gas due to a carb problem and they are the common up draft carbs. Air cleaner tubes go above manifold height so gas fills the carb then the manifold and then into the engine and fill the oil pan

Bob Bancroft · Feb 10, 2016

Maybe the idea that they wanted, or assumed the exhaust should go out the top, like a chimney? So the exhaust manifold got put on top, the intake on the bottom, and the rest is history?

2underage · Feb 10, 2016

To prevent the gasoline from a leaking carb from running down into the crankcase and diluting the engine oil. As simple as that.

NoNewParts · Feb 10, 2016

(quoted from post at 23:43:44 02/09/16) Why did most vintage tractors have up-draft carbs?
I started working with tractors 70 plus years ago and I still haven't found out why.

Fred

better idea in its day.
Why design in a fuel pump when you already have a very efficient airpump(the engine).
Gravity the fuel to the carb, the airpump/engine will draw in the vapor.

Fire. You racers know the frantic problem when a Holley starts overflowing from a needle fault.
Updraft carb hanging low just makes a mess on the ground...if the throat drain filter is clean.

dlbuck · Feb 10, 2016

I have seen gas in the oil from a stuck needle in a John Deere MT.

Steve@Advance · Feb 10, 2016

In the very early days, simplicity was a key design feature.

Updraft eliminated the need for a fuel pump. Anything with age degradable parts, as in a fuel pump diaphragm, was a source of a potential problem. Once the vehicle left the factory, it was designed to be as field repairable as possible.

They required a lot of maintenance, but mostly limited to fluids, seal packings, belts, things that could be improvised from leather, made in a blacksmith shop, etc. Not many sources for replacement parts out on the prairies!

sotxbill · Feb 10, 2016

I AGREE... floats and needles were prone to sticking and tractors ran bad gas... So the updraft worked better in that environment. They prevented flooding, dilution of oil, hydro-locking, and fires by letting the gas drain below the exhaust manifold. ALSO kept carb low and helped avoid vapor locking from excessive heat and leaving a way for any gas bubbles to move upwards to the tank without being trapped.. pending fuel line design.

[b:451e353029] Improvements in carb and float technology[/b:451e353029] allowed the addition of fuel pumps, and fuel pumps, allowed the elimination of vapor locking due to higher pressure lines having a higher boiling temperature. And then this allow down drafts, meaning that now (heavier than air) mixtures could flow downwards and give better starting and performance on newer designed engines. 12 volt systems allowed longer and faster cranking, allowing better starts.

up draft carbs.

F.E.Bear

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Sam Womer (PA)

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gene bender

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centash

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Paul Janke

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Roger in Iowa

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David G

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Sprint 6

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old

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