29-27 fuel leak - need guidance

[jps]

I bought a 1929 model 27 about 2 weeks ago. It drove OK for a few days, but on Sunday it started leaking a lot of fuel. I got nervous and shut off the car without identifying the exact source although it appeared to be near the carburetor. I checked, tightened, or replaced a few connections and tried again today but got the same results although I kept the engine hood open to identify the leak source. I then read a bit about the carburetor in the manual to help identify its parts. I determined there was fuel flowing out of the air adjustment screw at the top, and fuel seems to also flow all the way to the air intake filter at the other side of the carburetor because I saw dripping there later too. There is pretty much a constant stream of fuel that flows down on the ground, but only with the engine running. There is no leak with the engine stopped. The engine starts and runs fine. I start with the choke full out and push it almost full in when the engine starts. I did not notice any leak the first few times I drove the car.

Also, it may be important to mention these other facts: The carburetor adjustments were checked by a mechanic before I bough the car. The mechanical fuel pump is not currently in use - it is there but no fuel connections are made to or from it. There is an electric fuel pump that is always on with the ignition switch. There are two new fuel filters - one back with the pump near the fuel tank and the other in the engine compartment before the carburetor. The fuel line from the second filter into the carb inlet is 5/16" line and I think the original line probably was either 1/4" or 3/16" between the mechanical pump and the carb. I did change out the engine compartment filter - it was a plastic one and now I put in a metal one, but this was done today, AFTER the original fuel leak yesterday.

Here are my questions:

1) Could there be too much fuel flow into the carb due to bypassing the mechanical pump with an electric pump that is always on?

2) Is the increase in fuel line size to 5/16" causing too much fuel to flow into the carb (the filter holds a small reservoir of fuel to supply the bigger tubing)?

3) Could there be a membrane, diaphram, disk, check valve, etc in the carb that is leaking to allow fuel to flow into the air inlet before the correct location (I do not know anything about the internal construction of the carb)?

4) Does the carburetor need to be adjusted to reduce the fuel allowed in? There is a basic adjustment procedure in the manual that I have for the car to adjust the air screw and the gasoline screw.

5) What do you think is the problem and what should I do next? I did not see any leaks in the fuel line going into the carb.

Thank you.

[ROD W]

jps

Check the cork float in the float chamber, It may be saturated with fuel and not closing off the needle valve. Take off the float chamber cover and you can see if the float and needle valve are working. Also the electric pump may be too high a pressure.

My car also had an electric pump installed when I bought it and it was flooding. Changed it back over to the vacuum tank. I don,t know what pressure the mechanical pump works at on the 29. There is no need to adjust the air screw or the gasoline screw if the car was previously running well.

Edited May 27, 2014 by ROD W (see edit history)

[jps]

Thanks for the advice Rod. I will try that this weekend.

Was the cork float originally coated with something (lacquer or varnish or shellac) to keep it from absorbing fuel? Maybe that has worn away?

I will also see what I can do about the electric pump.

[Mark Shaw]

The Marvelous Marvel Updraft Carburetor

By Mark Shaw

One of the most condemned and abused Buick components from the teens to the early thirties is the infamous Marvel Carburetor. Many Buick owners have plugged their exhaust heat systems and either replaced their original Marvel Carburetor with a Zenith, Carter BB1, or some other updraft carburetor. Some just gave up and flipped their intake manifold to install a more fuel efficient downdraft carburetor to improve both performance and mileage in their cars.

I still run original Marvel carbs in most of my Buicks. I use full choke from a cold start & usually need to keep the choke out 1/3 to 1/2 until the engine warms up. This seems to be normal for Buicks with or without working exhaust heat systems. Mileage & performance is not as good as downdraft carburetors, but I believe that keeping these old girls going with their original equipment is part of the pleasure in driving and maintaining these old cars.

The most common cause of Marvel carburetor problems seems to be the need to replace the 70-80 year old cork float. I know that many prewar Buick owners will struggle to get their Marvel carburetor to work properly with these old dried up cork floats. It would be rare for such old cork floats to work reliably, so they must be either be replaced or coated to prevent saturation.

The purpose of the float is not just to start and stop fuel flow to the engine; it also continuously maintains the correct fuel level at the jets. The jets are carefully sized to atomize and supply the correct volume fuel & air to the engine at all operating speeds. If the fuel level is too high or too low, the jets will either starve or flood the engine. Sound familiar?

I have several old books and manuals that troubleshoot and/or explain the various designs and theories of how all kinds carburetors work. I also have Harold Sharon’s book “Understanding Your Brass Car” that explains how any do-it-yourself amateur can replace the cork in an updraft carburetor to drastically improve performance. Harold explains in simple terms how you can use “Crazy Glue” & wine corks to make a replacement cork float to fit in almost any carburetor. He also states that coating the cork is not necessary. I expect that gasoline additives & ethanol in modern gasoline would probably dissolve any of the old recommended shellac coatings and gum up everything anyway. But, I know that model airplane dope or Crazy Glue can be used to seal cork floats.

Another relatively common problem with Marvel Carburetors is with the main jets that develop small cracks. These cracks can easily be soldered to solve the problem. Just run a drill bit with the same inside diameter through the jet after soldering to make sure excess solder does not restrict flow.

The ultimate alternative is to flip the intake manifold and bolt on a Rochester carb from a "stovebolt six" GM engine. There are several models of this carb...with and without automatic choke. My son is considering doing this on his 29 Buick. If you keep all the original parts, this modification can easily be reversed if you or the next owner prefers to show the car.

[ROD W]

jps

Your cork and needle valve would look similar to this one. You can make a new cork float or coat the old one with epoxy as per Marks previous post

[jps]

Thank you Mark & Rod. That is the info I need to know.

When I open up the cover to get at the float + needle, is there a gasket under the cover and will I need to replace it? Or if I am careful can I re-use the old one?

Thanks again - this helps a lot.

John

[ROD W]

John, Its just a thin paper gasket under the cover plate, cut a gasket out to the same size as the cover and make a hole in the middle for the button. I don,t use gasket sealent on this.

[Bob Engle]

Mark and Rod are right on on the carb setup. With the vacuum tanks, fuel pressure to the carb was by gravity. the tank is 2 to 3 feet above the carb and at 1/2 pound per foot gravity pressure you only have about 1 to 2 pounds pressure at the carb. Even the early early fuel pumps only produce about 2 pounds of pressure. I would regulate the pressure from electric fuel pump so excess pressure doesn't overwhelm the float and needle valve.

With respect to fuel line size, too small is the only problem. The fuel pump will determine the amount of fuel delivered to carb.

Working with these old fuel systems is part of the fun. Enjoy the ride!

Bob Engle

[jps]

OK, I just took off the carburetor and the top cover. I was a bit surprised because the float is not cork but a small brass "can" that has been manufactured out of thin brass sheet and soldered together (see photos below). There is a dent in the can and fluid that appears to be sealed inside the can. All I can guess is that someone made a replacement float and added the liquid inside to get the right weight. I can't tell if it is working correctly or not. So my next idea is to get the book Mark mentioned (I already sent payment) and read about how to make a new one from cork. However, since the brass arm that connects the needle valve to the float is soldered to the brass "can", I don't know how the arm was supposed to attach to cork.

Also, there is a screw in the cover plate that looks like it might be adjustable to act as a "stop" for the float to limit its high point in the bowl. Did the original float/cover have this? It does not look original.

I called a local place that says they sell cork, but they don't have anything big enough to make a float out of a single piece of cork. It seems like I could just glue a few widths together to get the size I need - any problem with that?

[Bob Engle]

I got my cork at a hardware store that had a selection of cork stoppers. One was about 2 1/2 " in diameter and 1 1/14" thick. I do seal them with model airplane dope as it is alcohol proof. With all the home made stuff on your carb, I would be concerned about whether the jets have been monkeyed with. The length and jet size is critical to good operation.

Bob Engle

[raydurr]

Look to Restoration Supply Escondido CA. Page 12 of their online catalog, has nitrophyl floats for Marvel carbs. These guys also stock cork and nitrophyl material for float fabrication . Another source for what you need is Bobs Automobilia . They sell Marvel floats and the gaskets you need. The carb kit they sell has a float included. Good Luck!

[ROD W]

John, There is usually a button in the middle of the float chamber cover, which can be pushed to check that the float chamber is full. When turning my car off, I always turn the vacuum tank off and let the motor run till the float chamber is empty, So when starting I jiggle the button to ensure the float chamber is full. This probably can not be done on the 29 with a mechanical pump. Your float chamber is a different shape to the earlier cars, but on mine the float is 2" wide, X 1 5/8" and 3/4" thick with a 3/16" gap between the float and chamber wall. But if you can pick one up at Bobs, that would be the way to go. A brass screw holds the float onto the arm.

You don,t want to restrict the movement of the float up and down as it needs to fully raise to shut off the needle valve

[bradsan]

John

Fluid in a metal float is usually an indication that they are leaking; which means the float has sunk and is letting too much fuel in via inlet valve. Not sure if your original was cork or metal but you can test you current float by putting it in some hot water. If there is a hole ,any air inside will expand and bubbles will come out. If air can get out, then fuel can get in. Depending on the condition of the float, this can be fixed easily. Just google it. . Basically, gently heat the float to expel the fuel inside and then solder the hole up. Presumably, the car was running at one time with the float it came with.

Brad

[Mark Shaw]

Get your wife or girl-friend to empty the wine bottles.

Use Krazy Glue to make one large piece of cork.

A sander or your grinder works well to shape the corks and make a float to just fit into the float bowl.

Make sure it is tapered to move up and down freely.

You can coat the entire float when you are done to protect it from modern gasolines.

[jps]

Thanks everyone for all the good advice and help. I found out a lot about carburetors over the past few days - probably many of you know this already but now I do too. Fortunately I work with a mechanical engineer who worked for an engine mfr and knows a lot about carburetors as well, so I am getting a lot of consistent answers whch makes me feel better. However, I found out something about my carb that may not be ideal. Here is a summary:

From The Carburetor Shop (link from Buick Club website) - there are 2 casting #s and 2 bowl #s each for 1929 Standard & Master Marvel carbs. I have a 10-103 casting and a 10-706 bowl. The casting is correct for a Standard but the bowl is for a Master. The Carb Shop says that the two should not fit together, and that they wouldn't know what rebuild kit to send me if I wanted one.

Also from the Carburetor Shop - brass floats were a legitimate aftermarket "improvement" to the cork, but they can leak and gets dents easily. The guy I work with knows about brass floats and confirmed the repair procedure listed on the Carb Shop web site, and from bradsan's post above.

I was considering getting all new gaskets, needle & seat, etc and go back to a cork float but now I just think I would like to keep it simple and only repair the brass float. In the future I will look for a complete standard carburetor to replace the patchwork carb that I appear to have. If I can't fix the brass float then I will make a new cork one.

I really appreciate everyone's help.

[Bill - 29 Buick]

John:

Late to the discussion but I'd bet your leaking problem is caused by either / combination of: sinking float (pin-hole in your brass one), bad needle and seat and using too high a pressure electric fuel pump. All are fixable. Also, the answer to your question on bowls for 29 Master and Standard carbs is a bit complicated. There are 3 different cast iron pieces: Master 105, Standard 103 and a non-numbered piece that is standard on the top and Master on bottom. So, there was a standard and a master pot metal bowl / lip and then, at some point in the production, they shifted to use all master bowl / lips with a Master cast iron upper piece for the Master engines and a Standard /Master cast iron upper piece for the Standard engines. This adapted piece has the Standard dimensions on the top to fit the heat riser and Master on the base to fit the master bowl / lip.

Bill McLaughlin

1929 McLaughlin Buick Roadster

[jps]

Thanks Bill - that last bit of info is very interesting any could explain what I have. However, if I understand correctly then my casting should be unmarked yet it is cast with 103 on it. Is it possible that the first few combination Standard/Master castings were made with the 103 in place, and then they realized later that they should remove the number? That seems to be the best explanation for what I have.

I will fix the float first and try it. I made a little stand to hold the carburetor so that I can add fuel at the inlet just using gravity and see if the float closes or not. If it does then I'll re-install in the car. If not, then I can replace the needle & seat. I won't change the fuel pump unless the leak re-appears after the float and/or needle/seat fixes are made. If needed, I saw a low-pressure (2 psi) 6V pump for sale in some of the literature you sent to me earlier.

So if I do have the Standard/Master casting and I wanted to replace the needle/seat or do some kind of rebuild in the future, I assume I would need the needle & seat & top cover gasket for a Master bowl but a standard gasket for the manifold-to-casting connection (assuming the needle/seat for a Master is different than for a Standard?).

[Bill - 29 Buick]

John:

No idea if some of the Standard / Master castings were still marked 103. I'd doubt it. I'd say you have an early standard cast iron piece and therefore have / need a standard carb bowl. I'm trying to get the numbers marked on the bottom of the carb bowl lip for master and standard.

The carb pot metal top and needle and seat are the same (master and standard) but you'll need a standard gasket between cast iron carb piece and bottom of heat riser.

Note: if you had one of the late Standard / master set-up, you'd need the standard jets (which likely have smaller holes than the Master).

Bill McLaughlin

1929 McLaughlin Buick roadster

[jps]

According to www.thecarburetorshop.com the numbers for Marvel castings and bowls go like this for 1929 Buick:

casting # 10-103 => Standard

casting # 10-105 => Master

bowl # 10-704 & 10-705 were used with 10-103 (Standard)

bowl # 10-706 & 10-707 were used with 10-105 (Master)