cjmarzoli

Keeping gas in a Marvel updraft carburetor when parked. Where does it go?

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I have a 1931 Buick model 8-67.  Has the marvel updraft carburetor.  If the car sits for more than a day or two, the  bowl becomes virtually empty which makes it difficult to start as the carb bowl must be filled by cranking  and cranking before the engine gets any gas.  I have a loop in my fuel line to the carb and installed a backflow preventer just behind the carb so where is the fuel going?  I don’t think it could possibly all evaporate that quickly.  I don’t see any evidence of it leaking out or running out the front.     Anyone else had this issue?   Does anyone have a good method for pre priming the bowl when it does empty?  There is a very small vent hole on the top, perhaps there is a way to inject fuel through there.  You cannot just dribble it down the top like you can on a modern downdraft unit.  Thanks!

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Posted (edited)

Gas is probably boiling out from high under hood temperatures. It’s called hot soak. On an updraft the fuel will just turn to vapor in the air, and sometimes drop out the bottom of the air filter horn/neck. Common issue on many pre war cars. Many people run electric boot pumps to prime the carb.

Edited by edinmass (see edit history)

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I have a 31 8-66S .  The marvel carburetor has a vented bowl and when you shut the car off, especially if it's hot, it's gonna evaporate the fuel out of the bowl.  I've been avoiding that so far because my car is not ready for the road so instead of putting gallons of gas in the original tank that I know will become gallons of stale gas with lots of water in it I've been running my car on a small outboard tank with a rubber squeeze primer bulb.  The only ways of avoiding this problem if the car is going to sit for more than a few hours is either an electric fuel pump or filling the bowl with fuel from a plastic squeeze bottle.  I've been think of clever ways to use the latter and adding fuel to the bowl right thru the vent hole in the bowl cover so I don't have another electric gizmo on the car or have to take the bowl cover off.  Our cars do have a drain tube that screws into the bottom of the air filter and drains fuel overboard next to the road draft tube to take care of fuel that boils out of the carb and floods the air horn of the carburetor.

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Did gas in the 1930's not evaporate?   People had to depend on these cars so you'd think the carbs would hold gas for a few days at a time at least.  When an electric pump is installed, does this supplement or completely replace the original mechanical pump?    Where on the car would the electric pump typically be mounted?   Str8-8-Dave, yes I have the drain tube on the air cleaner.  I would prefer to avoid installing an electric pump if I could prime the bowl easily by hand without taking the bowl lid off.  I'll keep brainstorming and let you know if i find a solution and you do the same, thanks!   Maybe a very small plastic tube that could be inserted through the bowl vent.  I'll have to study it again.  I forget how small it actually is. 

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Gas in the 30s was not as volatile, so did not vaporize as easily. Todaus gas is formulated for fuel injection, under high pressure, and does not set in a vented bowl in the hot engine compartment.  Electric priming pump will work.

 

  Ben

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Posted (edited)

I will knock on wood but my 31, 66s, does not have that problem. If cold it needs a second or two of choke then off it goes, no choke when warm. I do drive it often but if it has sat for a few weeks it will start quickly using the choke.The fuel line from the pump to the carb has the loop in it and the carb is the original 10-795. I can't imagine it makes a difference but it does have the late 31 air cleaner.

 

 I did have to block off the heat riser, replaced the tubes, and installed a new intake/exh. gasket to cure a lean when hot running problem.

 

Dave

 

edit -I have been using no ethanol fuel for the last year or two. 

Edited by Dave39MD (see edit history)

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Any fitting that might have a minor leak near the carb will allow the gas in the line to siphon back to the tank. Maybe a back flow restrictor at the tank might be more useful if this is the case. 

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Thanks.  I did installed a backflow preventer in the line just behind the carb and it didn't help the issue any.

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Thank you all.  I ran the car today.  It had been 3 days since I drove it and the bowl was empty before I started it up!    My smart idea was to cap the vent on the carb lid after I got done driving the car to prevent some evaporation.  I found a small rubber cap that fit perfect over the vent dome.  Well, it didn’t work.  I placed it on after my excursion and immediately heard a hissing noise.  Then gas started oozing out of the top bowl gasket under the cover and dripping out of the front air horn between carb and air cleaner.   I quickly removed my cap but it kept dripping slowly out the air horn for at least another 10 mins.  I’m not sure if it would have dripped out the air horn (front of carb) had I not capped it, but if it does, that is where some of my gas is going.  Not sure why the bowl was pressurized after I shut the engine off enough to pump gas out after I capped the vent port on the bowl cover.  Temperature Expansion?

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On cars with fuel shut offs I usually cut the fuel just before I enter the building. By the time I park it it’s usually empty....thus no leaks. Some people install a six volt electric shut off in cars today. They kill the fuel in the same way, draining the carb and taking the pressure out of the fuel line. My guess is upon shutdown under hood temperatures increase and fuel not only pushes out of the bowl, but the fuel line pressure is bleeding down. A properly installed boost pump will be your best bet. Run it for a few seconds before start up to fill the carb.

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Dave39MD brought up a good point, he uses ethanol free unleaded gas.  While regular unleaded is cheaper, easier to find and is higher octane than the best fuels of the 30's it has ethanol alcohol in it, 10% or possibly more and it absorbs water like crazy in our vented fuel systems and evaporates much faster than ethanol premium gas does.  Ethanol free fuel may help.  I stopped using ethanol fuels in my car because I also noticed 2 things, one, the fuel turns from nearly clear with a yellow cast to maple syrup dark brown in the glass sediment bowl on the fuel pump in a matter of days and when I started the car there was water dripping from the manifold to heat riser pipe.  The water business stopped when I switched to Shell premium form a local station because it is ethanol free.  I'm a stubborn old guy that has not blocked off my heat riser, it is complete and it works so I am particularly interested in keeping the condensate to a minimum to avoid rust.  I'm sure at some point I will wind up blocking off my heat riser but being fascinated with mechanical oddities and having healthy enough parts on my car I was able to research and figure out how all that linkage is supposed to work and made up a heat riser system that works for now at least. 

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Posted (edited)

Even if not running E10, the blending stocks and added chemistry change the specific  gravity of the fuel, which will effect float height, and well as other things. What we buy at the pump today is a far throw from what we were pumping pre 1975.

Edited by edinmass (see edit history)

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You could try adding some kerosene or stove oil to your gas to lower the boiling point. Gas back then was low octane, and oilier than today's gas. As others have pointed out it is formulated for fuel injection in a sealed system and evaporation and vapor lock are no longer a concern. With a low compression engine you can add 10% to 25% kerosene. The engine will run better and cooler and develop more power.

Also, here is a Marvel manual, it is for Nash but maybe your carburetor is similar.https://www.gutenberg.org/files/27298/27298-h/27298-h.htm

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Does an additive like Sta-Bil lessen the evaporative quality of modern fuel by any measurable or meaningful amount?

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I am installing one on my Dodge too. Advise I read says mount it lower than the tank in a spot near the tank because these pumps are better at pushing the fuel. Don’t put it above the exhaust system in case a leak happens. I’m putting an on/off switch on mine to use it primarily to prime the system.

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I don't understand why there's always push back against using electric pumps to assist with this exact situation. It isn't a crutch or band-aid, it's adapting the car to a different set of operating circumstances which are a reality today. We bypass the carburetor heater assemblies to keep the carburetors cooler, why is that not viewed as a crutch or band-aid? After all, the car ran fine when it was new with all those things operational...

 

Oh, that's right, it's because as Ben wisely points out, TODAY'S GAS EVAPORATES AT ROOM TEMPERATURE and gas from decades ago did not.

 

When you shut off the engine, coolant stops flowing and the fan stops blowing air across the metal parts. Temperatures skyrocket. That modern gas, with ethanol or not, boils at 170 degrees or thereabouts. It may even be boiling while you drive--I can sometimes hear it percolating in the carburetor of my '29 Cadillac while the engine idles. When it boils, that's the liquid gas turning to vapor and escaping through all the various vents and openings on the carb. It's gone. It isn't draining, it isn't magically jumping up to the float valve, pushing it open, and heading uphill back to the gas tank against the weight of the gas in the tank, it's EVAPORATING. Next time you fill your lawnmower, sprinkle a few drops on the ground and watch how quickly they vanish.

 

An electric pump will put fresh fuel into the carburetor bowl and facilitate quicker starts, which is helpful both after a period of inactivity and during a hot start. I'd much rather have a mechanical solution to the problem rather than trying to mix up my own gas blend with a higher boiling point and/or lower Hvap. A pump will also help when you experience problems on the road due to heat. As I said, my Cadillac can boil fuel as it runs, but by using the electric pump it has never stopped running or failed to get us home. 

 

An electric pump is not a crutch or an admission that the car is broken or that you need to fix something. It's a work-around that effectively deals with a problem they didn't have when the car was new. Hell, they only cost $40 and are very easy to install. Why WOULDN'T you use this tool to make your car work better or have it on-board just in case?

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Matt - I am not one pushing back, and in fact have electric pumps on ALL my collector vehicles (well, not the John Deeres), however; here is some information from my website:

 

 

There are a number of reasons car enthusiasts look at electric fuel pumps. The most common being hard initial starting due to modern fuel evaporating from the carburetor overnight. Whatever the reason, there are a number of considerations when deciding to install an electric fuel pump:

 

(1) Is the installation legal? Electric fuel pumps should be installed with the permanent wiring activated by something like an oil pressure switch, such that in the event of an accident and the driver becoming incapacitated, the electric fuel pump would automatically be turned off. Temporary wiring to a push button can be used to activate the pump and fill an empty carburetor. Release of the pump button will kill the pump, but there will be sufficient fuel in the carburetor bowl to start the engine and run until the oil pressure comes up to activate the permanent wiring.

 

(2) Does the pressure produced by the pump fall within the parameters required by the carburetor? This question has more than one issue and should be considered carefully. Think of the difference in methodology of the electric pump vis-à-vis the stock mechanical fuel pump. The electric pump is more or less a constant pressure, constant volume pump (assuming the GPH of the pump is greater than the maximum demand of the engine). The stock mechanical pump is driven by the engine; therefore volume, and to a lesser extent, pressure, is a function of the RPM of the engine. Thus it is quite possible, if the wrong electric pump is chosen, to have a pump that floods the engine at idle, and has insufficient volume to maintain proper carburetor bowl lever at wide open throttle.

 

(3) Because of (2) above, many enthusiasts opt for an adjustable inline regulator. Many of the less expensive regulators regulate pressure by regulating volume. Thus getting the pressure sufficiently low to not flood the engine at idle then limits the volume necessary to drive the vehicle at highway speeds. And just because the dial on the regulator states some number, do NOT ASSUME that the output pressure from the regulator is what the dial indicates. ALWAYS check the output pressure with a calibrated fuel pressure gauge. A return fuel line from a connection just before the carburetor back to the fuel tank is MUCH better at reducing idle flooding than a regulator.

 

Summary – the electric pump IF properly selected and properly installed, may be of benefit to the enthusiast. Do it wrong, and one had better check with their insurance agent about fire BEFORE installing the pump!

 

Jon.

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Posted (edited)

As far as improper installation of electric fuel pumps......I know personally of three car owners who lost their garage.....and one his home also. All electric pump related. Pressurized fuel systems from 1905-1925 are often a bomb on four wheels......like on the tour at Amelia this year. The float sank, and the gas kept coming from the tank under pressure to feed the fire...... The owner did not understand he needed to bleed off the air pressure from the filler. They went through five large extinguishers and it kept burning. Fire truck put it out. The mess from the powder was beyond belief. On my 14 Cadillac with a similar system I had a 6 volt Electric valve to vent to atmosphere on the fuel system so when I shut the car down the pressure would dump to zero immediately. I have only seen one other collector do this. Certain cars are more susceptible to Fire than others. Cadillac is number one. I carry four Haylon extinguishers When driving any Cadillac. Two small, and two large. I have recently installed element fire extinguishers in every car along with the Haylon. Look them up and watch the you tube video. 

5B0B9811-8376-48C5-8FD4-40603264B875.png

Edited by edinmass (see edit history)

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6 volt low pressure pass through  pump on a momentary toggle to prime before start, problem solved. I had the same issue before, now with 2 seconds on the switch she starts right up and no worries about over pressure or fuel pumping uncontrollably in an accident or failure

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Posted (edited)

The problem with the toggle Switch on the pump Is people forget them. I watched a $4 million car burn 18 months ago because of a toggle switch. Fortunately we got it out with only the scorch to the engine and hood. 
 

 

PS- any car with a stock carb and a vacuum tank that has an electric fuel pump on it IS A DISASTER WAITING TO HAPPEN........no matter what ANYONE says or thinks. And yes, I have over 50k miles on vacuum tanks........with modern fuel in the last twenty five years, all bone stock. The systems work ok today, even with modern fuel, without boost pumps or primary electric pumps.

Edited by edinmass (see edit history)
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Posted (edited)
25 minutes ago, edinmass said:

The problem with the toggle Switch on the pump Is people forget them. I watched a $4 million car burn 18 months ago because of a toggle switch. Fortunately we got it out with only the scorch to the engine and hood. 
 

 

PS- any car with a stock carb and a vacuum tank that has an electric fuel pump on it IS A DISASTER WAITING TO HAPPEN........no matter what ANYONE says or thinks. And yes, I have over 50k miles on vacuum tanks........with modern fuel in the last twenty five years, all bone stock. The systems work ok today, even with modern fuel, without boost pumps or primary electric pumps.

 

THIS !!!!!!!!!  I've lost count of how many times I've said the same thing over the years. And still I see cars with a electric pump feeding the vacuum tank because whoever installed it didn't understand how they work and the problems that can cause. 

 

Some vac tank setups, like many of the Stewart Warner,  have the vent tube pointing right down at a hot engine parts. On some it's right above the exhaust pipe.  Turn on the electric pump, you not only risk flooding the engine back through the intake manifold vacuum supply line, you have raw gas squirting down at the hot engine parts. 

 

Vacuum tanks worked well when new and still work well when fixed by someone who knows how to properly do it. Like carburetors,  a quick cleaning and slap some gaskets in is not a proper fix. 

 

Paul 

Edited by PFitz (see edit history)

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Posted (edited)

There is nothing, I repeat nothing, more reliable and better than a mechanical fuel pump, metal lines, and a sock filter in the tank... IF you can get it to work.

 

I have been down the electric fuel pump avenue in just about every way possible, and I now avoid it like the plague.

 

IF you are going to do it, the best setup I know of is the one often advocated here that has a switch and is only used for priming.

 

I won't comment on other early systems like pressurized fuel tanks, vacuum tanks, etc.... except to say that there are even more possible pitfalls with a conversion.

 

People like to blame all the troubles on modern gas, and the boiling point of ethanol. I doubt it. Yes, today's ethanol-laced gas is crap. It rusts fuel tanks and eats fuel hoses and carburetor parts, But does it boil easier?

 

In the 1980s, due to limits on tetraethyl lead, gas was expected to have about 8-10 percent octane boost package consisting of some combination of Ethanol, Methanol, and MTBE. Methanol and MTBE both boil at an even lower temperature than Ethanol. The oil companies adjusted their "target" for reid vapor pressure according to the season. They adjusted for the season in the 50s, 60s, and 70s too. They probably still do today.

 

The 1920s are an anomaly, as gasoline was full of heavier portions (basically kerosene) because the popularity of the car was exploding and the refineries couldn't keep up.

 

Until I hear a Petroleum Engineer, one who works with Gasoline, (do we have any in here?) say that the target reid vapor pressure has changed significantly since the 1980s (has it?), I am not going to blame the gas.

 

Edited by Bloo (see edit history)

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The responsibility of operating a pre war car safely lies directly with the owner.  Not Understanding tire, brake, fuel system, and other limits on restrictions on safety and performance cause 99 percent of all problems and accidents. What I have seen driving down the road with people’s family in the car is beyond insanity. At one tour in the past decade, I test drove a car for someone. I never left the parking lot......the car was that unsafe. I immediately “downed the car” with the tour managers. Told them not to allow the car to join the event. They didn’t have the nerve to toss the guy due to weak backbones. The car did fail, in a very dangerous location on a mountain. Fortunately no one was hurt. 

Edited by edinmass (see edit history)

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Posted (edited)
18 minutes ago, Bloo said:

There is nothing, I repeat nothing, more reliable and better than a mechanical fuel pump, metal lines, and a sock filter in the tank... IF you can get it to work.

 

I have been down the electric fuel pump avenue in just about every way possible, and I now avoid it like the plague.

 

IF you are going to do it, the best setup I know of is the one often advocated here that has a switch and is only used for priming.

 

I won't comment on other early systems like pressurized fuel tanks, vacuum tanks, etc.... except to say that there are even more possible pitfalls with a conversion.

 

People like to blame all the troubles on modern gas, and the boiling point of ethanol. I doubt it. Yes, today's ethanol-laced gas is crap. It rusts fuel tanks and eats fuel hoses and carburetor parts, But does it boil easier?

 

In the 1980s, due to limits on tetraethyl lead, gas was expected to have about 8-10 percent octane boost package consisting of some combination of Ethanol, Methanol, and MTBE. Methanol and MTBE both boil at an even lower temperature than Ethanol. The oil companies adjusted their "target" for reid vapor pressure according to the season. They adjusted for the season in the 50s, 60s, and 70s too. They probably still do today.

 

The 1920s are an anomaly, as gasoline was full of heavier portions (basically kerosene) because the popularity of the car was exploding and the refineries couldn't keep up.

 

Until I hear a Petroleum Engineer, one who works with Gasoline, (do we have any in here?) say that the target reid vapor pressure has changed significantly since the 1980s (has it?), I am not going to blame the gas.

 


 

 

I have had extensive meetings with a professional chemist and “fuel engineer”. He worked for twenty five years at Sunoco in the R & D department.He also designed fuel systems for rockets at Morton Theyicall  (spelling?) Fuel is a chemical, with many, many added ingredients. Energy content,  specific gravity and boiling point have changed drastically over the years. Blending stocks and the carbon chain of all types of fuel are no longer anywhere near what they use to be. Most octane today is boosted up  by alcohol. On paper the modern fuel should act fine in any carbureted system.....that’s on paper. The smaller the displacement of the engine, the more likely you will have a problem. Stoichiometry is what rules Carburetion and fuel injection systems. The earlier the carburetor, the more difficult it is to properly modify it for modern fuel. Hint: very, very few people are capable of recalibrating a carburetor correctly. VERY FEW. Many try, and many ruin engines in their attempt to do so......after all, they read it on the internet. 

 

 

 

 

Edited by edinmass (see edit history)
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2 minutes ago, edinmass said:

Stoichiometry is what rules Carburetion and fuel injection systems.

 

That I can deal with (with a gas analyzer).

 

I am running a "taxicab" metering rod (2 steps lean) in the 36 Pontiac and would try another step leaner if the parts existed. This is with 10% ethanol fuel and I am only 780 feet above sea level. It runs great. The leaner I can get it here at 780 feet and still run good, the less trouble I figure I will have with the continental divide....

 

It really surprises me how little trouble I have seen with mixture strength when the fuel (10% Ethanol) is "leaner" so to speak.

 

It is the boiling issues mainly that I have never seen addressed. Some cars were always prone to vapor lock and/or percolation in hot weather. It was a frustrating problem to deal with back then, and It seems today nobody even tries, they just blame it on the fuel.

 

 

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