m-mman

Why updraft carbs?

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I am new to 1920s & 1930s cars so excuse me if this seems like a stupid question.

 

I have long history with 50s & 60s cars and understand them well.  

In an effort to experience an "old" car before I die, I have acquired a 1929 Cad and a 1926 Lincoln. Acquainting myself to the ancient technology has been a very steep learning curve.  Mechanical brakes, vacuum fuel systems, three brush generators, etc. are not things I have had any experience with, but S-L-O-W-L-Y I am beginning to understand them.  (and there are few 'old guys' around  who could explain things that I have been able to connect with)  I am working to learn the cars on their own terms and not 'improve' them. But some of the technology has me baffled. 

 

One question I have not found an answer to (and I have searched) WHY updraft carburetors???

 

Gravity pulls things down. The 1900s stationary engines that autos were based on seem to use side draft carbs at least.  Opposed engines seem to have downdrafts.

Either an inline or V type engine, why use an updraft? It either makes for a strange V type set up having the carb so deep in the valley, or in an inline it puts the air intake almost at the dirt road surface and without an air filter. 

 

By the early 30s most everyone seems to have agreed that downdraft was superior. What were the ancient automobile engineers thinking that caused them to choose an updraft set up from the beginning?

 

 

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I am no engineer, but maybe it had to do with flooding of the engine prior to perfecting the downdraft style carburetor. There may not have been a carburetor that could regulate the downward flow. Just a very wild guess.

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I think gravity is your answer. The lower the carburetor, the easier it is to deliver fuel to it. Prior to mechanical fuel pumps and vacuum tanks, carburetors were gravity fed.

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Updraft carbs can be very simple, as simple as a tube in an elbow.

Like many things automotive they started off simple with designs they understood. Also, updrafts tend to be less prone to flooding.  To much gas would just run out of the carb onto the ground rather than into the engine and flood.

 

They can be troublesome to set up, but remain reliable once set. Typically they have no venturis and just a standpipe at the lower part with an oriface and often a spring loaded flapper that initiates the necessary vacuum to pull gas into the airstrean to the engine.

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I second the concept of updrafts avoiding flooding. Over the decades that I've been going on old car tours, I can't tell you how many, many times I have seen cars puke a puddle of gasoline when they stop, slow down, start up, or sit and idle. But I also agree that gravity was important for getting fuel to the low-stationed carburetor, where engine vacuum could easily draw it inside the intake manifold. 

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What were they thinking?

 

They were thinking no one had invented reliable pressure fuel pumps!

 

I remember reading about one obscure make (the make escapes my memory at this time) that ran a small tube from the exhaust through a "filter" and then to the fuel tank to pressurize the fuel tank, and eliminate the need for a fuel pump.

 

Other makes used a squeeze-type bulb device that would pump air into the tank and pressurize the tank.

 

With the "perfection???" of the pressure fuel pump in the late 1920's, most passenger makes were quick (some quicker than others) to convert to downdraft carbs.

 

To me, VERY interesting to read some of the early car manuals to see ideas that were tried, and often discarded. My favorite of these is the Adams-Farwell engine. The carburetor with the steel/mica "capacitor" in the float bowl to warm the fuel is a close second ;) Maybe 40 years ago, I bought an early Dykes Encyclopedia at a library book sale. That night I started reading, and before I went to sleep, read that book from cover to cover. What interesting reading.

 

As far as an air filter was concerned, MANY cars were only driven from the farm to town on Saturday, maybe less than 10 miles a week! Interesting to look at some of the early centrifugal air filters, where the air entered the "filter" in a swirling motion, which was supposed to throw the dirt out of the air, and allow it to drop out an "air drain" at the bottom of the filter. Later filters filled the canister with horsehair lightly oiled, which the owner/operator was supposed to wash and re-oil weekly. Fascinating!

 

Jon.

 

Edited by carbking (see edit history)
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Carbking....you are a veritable fountain of carburetor information. Thanks for sharing. I love the Adams-Farwell engine!

Edited by keiser31 (see edit history)

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Very early cars used a wick carburetor! They had a fuel soaked wick and drew air around it, then this gasoline soaked air was mixed with fresh air to get a combustible mixture. They had a fuel lever and an air lever and were basically a constant speed engine because it was so hard to regulate the mixture once you got it you didn't want to lose it.

 

Lanchester used a quite sophisticated wick carburetor up to about 1920. They worked well and were reliable and were immune to the effects of dirt or water in the gasoline. They said their patent carburetor was more economical than the spray carburetor.

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35 minutes ago, Larry Schramm said:

I have been told that the first car with a reliable fuel pump was the 1929 Buick.

Studebaker 1928 all models had an AC mechanical pump. Was it reliable? The castings were similar to the Buick version so they probably lasted a few years before crumbling or breaking.

 

Auburn 1928 88 and 115 had an AC pump. Graham-Paige started in 1928.

 

All 1929 Buick had the same pump. Yellow Cab and Coach also had one in 1929. Chev started in the same year as did the Twin Coach Light Delivery.

 

These are the only pages of the AC book I have. Other makes could have started in 1928-9 too.

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Cadillac had an air pump built into the transmission for pressurizing the fuel tank. They needed some way to lift the fuel to carburetor level because of their V8 engine. Maybe other cars used the same system. Performance cars like Stutz Bearcat had a hand pump for pressurizing the fuel tank.

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Updrafts were always spilling a lot of gas.  Just think about all the gas that would get puked into the intake manifold when the carb. spits.  It is not only flooding but constantly washing the cylinder walls with raw gas and contaminating the oil.

Edited by nickelroadster (see edit history)

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Some more early mechanical pump adopters:

Cord 1929;   Duesenberg J 1929 had a SW;   Marquette 1929;   Oakland 1929;   Oldsmobile 1929;   Pierce Arrow 1929;   Pontiac 1929;  Reo 1929;   Stearns Knight 1928

 

So who released their 1928 model first?

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Duesenberg J used three electric fuel pumps, and one mechanical. Many early big cars used air pressure to the tank to deliver fuel, the earliest I remember seeing in person was 1908 or 1909. Air starters were installed by 1910 on BIG cars. Winton and Pierce come to mind, and I think Chadwick also used them. Vacuum tanks are very reliable, and I have driven tens of thousands of miles on them. 

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All Graham-Paige cars used the AC mechanical fuel pumps from 1928 on.  I have a 1928 and a 1929 still running on the original AC fuel pumps.  

 

Back to the comment on how often they ran;  My 1929 Graham-Paige owners manual recommends oil changes at "500 miles or annually, whatever comes first".

 

The updraft mechanical accelerator pumps are horrendous!  A couple pumps before the engine is running will have gas running out of the carburetor like a race horse with a bad bladder.  ALWAYS ONLY USE THE CHOKE to start an engine with an updraft carburetor.   Vacuum accelerator pumps solved that problem.

 

Jon gave me the "ONLY USE THE CHOKE" advice a few years back best old car advice I have ever gotten!  Thanks again!   

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2 hours ago, Graham Man said:

Jon gave me the "ONLY USE THE CHOKE" advice a few years back best old car advice I have ever gotten!

 

Yep, works for me too. I use full choke and just a smidgeon of hand throttle to start my Dodge 8. Once started, i add a bit of hand throttle and push in the choke a bit. Keep off the loud pedal until it is running properly, for exactly the reason given. It has a downdraft carb. but a pretty ordinary one according to Jon Carbking.

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Thank you all. 

Understanding the way things work (technology) seems to be much easier going forward ("These are the improvements") than going backwards ("Why did they do that?") 

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One of my favorite things about the old cars is trying to understand what they were thinking when they designed and built them. 

 

It is hard to believe a 1932 Duesenberg Speedster was todays Bugatti Veyron (technology)...

wait... scratch that, I would still take the speedster and it has two updraft carbs...

 

 

Image result for duesenberg speedster

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8 hours ago, Rusty_OToole said:

On the same car?

 

Yes Rusty, three electric and one mechanical. 

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By the way. with your '29 Cadillac you have chosen one of the most difficult carbs to adjust and keep in adjustment. You will learn a lot.

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"three electric and one mechanical."

 

I am going to go out on a limb... but low pressure and high volume is an engineering nightmare, going from idle to full throttle on a supercharged dual carb 420 CID engine without running out of fuel would be a huge problem.  Huge engine with lots of heat...how do you keep the fuel from overheating?

 

I hope sometime in my lifetime I will get the chance to drive a Duesenberg.  They were the engineering standard, at 25K new that is 400K in todays money.

Edited by Graham Man (see edit history)

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I am not familiar with the 29 Cadillac carburetor, I took Jon's advice and found a Carter 289SD for my 1929 Graham-Paige 322CID eight.  Awesome carburetor, zero problems (just use the choke to start it), starts right up every time, original AC mechanical fuel pump, always use non-alcohol fuel!

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