Marvel carb questions

[humber349]

Hi all,

I have got my Marvel carb on the kitchen table and I think I am beginning to understand how it works. Looks like I can leave the heat damper closed.

The automatic air valve flap thingy does not close completely. It only moves about 1/4" and stays about 1/4" open. It this correct or should it close right up?

I do not have the adjusting screw or the spring for this air valve. Anyone got a spare one I can buy or borrow to have them made please?

Looks like there is something missing in the corner of the float chamber. What should be there please?

The cork float doesn't look great. Can we buy new ones?

thanks http://1928buick.wordpress.com/

Edited September 17, 2011 by humber349 (see edit history)

[Guest outlaw car man]

This might help. Best I can do.

OCM

[Leif Holmberg]

Tell me your email address and I will send you some pictures from my parts book.

Leif in Sweden.

[humber349]

Thanks Leif

humber349@aol.com

[jscheib]

Phil,

You can most likely ignore the heat exchanger from the exhaust, as most of these early cars are no longer used year round when it is desirable to heat the fuel mixture when the weather is cold. However, if you want to use the car near year round you might want tye exchanger to operate. Mine is a '32, but I think the operation is quite similar, and it is quite complicated to operate.

I think elsewhere on the forum, some old stuff, there was messages about using a metal float to substitute for cork, but I am not sure where to find it. Others may be able to help you with that.

John

[carbking]

The airvalve MUST close completely.

Look at the bottom of the airvalve. The lower edge is probably binding against the spacer block. The spacer block is made of a very inferior grade of zinc alloy that "grows" with time. Generally, one may remove the two screws holding the spacer block, remove the spacer block, and then sand the flat edge of the block using a piece of sandpaper on a flat piece of glass. The object is to keep the block perfectly flat and level.

There should be approximately 0.007 inch between the lower edge of the airvalve and the flat surface of the spacer block.

Jon.

[Mark Shaw]

The Marvelous Marvel Updraft Carburetor

One of the most condemned and abused components in Buicks 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.

[humber349]

Thanks everyone, great forum!!

Leif sent me the parts list and I think these are missing from my float bowl-

M-168-4 metering pin link

M-84-44 metering pin jet

M-173-519 metering pin assembly

I think M-84-44 metering pin jet is still in the carb, but I suppose a new one would be a good idea. Thanks Leif

Thanks Jon- looks like the screws in the spacer block have been there 83 years and are not likely to come out any day soon, and heat and drilling will just cause more damage. I might try a careful light sand where it is.

Thanks Mark. I would like to try the Rochester option if I can find one.

Phil

Edited September 18, 2011 by humber349 (see edit history)