1925 standard six 25-20 marvel carb 10-11

[1956cody]

My 25-20 has a Marvel 10-11 carb on it with at least a bad float. I am seeking direction on what to do as I can  not seem to find any information on the great web regarding this particular model. I did speak to CarbKing and he thinks a down draft carb may be the way to go. I would be most appreciative of possible fixes/alternatives. Thanks in advance, Frank.

[Hubert_25-25]

I would fix your carburetor.  You can get the parts you need from Bobs's Automobilia.  He also has a service book. 

http://bobsautomobilia.com/shop/carburetor-items/

http://bobsautomobilia.com/shop/literature-and-decals/carburetor-marvel-service-booklet-1925-33-.-cm-253.html

 

Here is some additional carburetor information.

Hugh

 

Motor Tune up.pdf, MTU Page 18.pdf, MTU page 19.pdf, MTU page 20.pdf, MTU page 21.pdf, MTU page 22.pdf

[Mark Shaw]

Once again, here is my take on Marvel Carburetors:

Marvel Carburetors

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 Carburetor 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 older they are the more simple they are... If you have Marvel carb issues, first give it a good cleaning and check the cork float. Replace it if needed and set the fuel level just below the top of the lower jet. Make sure the air spring (inside the big adjustment knob) has a bulge in the middle or verify that it is original. If it is a straight spring, it may be the wrong spring. Set the big knob even with the tang and open the bottom fuel screw about 1 1/2 turns to start. It should start and idle with these settings....

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 struggle to get their Marvel Carburetors 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 fuel to supply the correct volume of fuel & air to the engine at all operating speeds. If the air control knob is not properly adjusted or 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 potential problem with Marvel Carburetors is with the brass jets that sometimes develop small cracks. Plug one end of the jet with your finger and suck or blow to determine if there are 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 carburetor from a "Stovebolt Six" GM engine. There are several models of this carburetor 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.

__________________

[Bob Engle]

I would be careful on the wine cork float idea.  Many modern wine corks are made as a composite to assure better sealing.  These corks are a more dense material.  Restoration Specialty Supply sells a synthetic material that can be easily shaped.  This material eliminates any concerns about the float absorbing fuel.  

 

Bob Engle

[Guest]

I agree with Mark Shaw completely.  I have 500,000 miles on my Pontiac's original Marvel carb.  Needle and seat replaced in 1962 and a new float made in 2005.

By the way e bay and several hobby shops sell small blocks of real cork.  The one I bought was about 1 1/2 x 2 x  6 and cost less than five dollars.  Why play around with corks and glue.  (sorry about mentioning Buicks little sister)

[dibarlaw]

Having rebuilt my own 1925-25 Marvel carb 2 years ago and it was performing well up until last November. Since then I have had all the previously mentioned problems. I have tried to address each fix independently to zero in on the true culprit. But I am still having issues. Even dealing with possible ignition sources. IE. new coil, points, plugs, condenser. Compression check and re-timing. After I replaced the new condenser (that was found to have the forked lead on the copper ribbon shorting to the breaker plate) it would at least run without backfiring. But still the idle is rolling no mater how the adjustments are. I have re-checked the sleeve for leaks. Re-fit the dash pot valve to venturi block according to the Marvel Book (they do change,  that wonderful die cast). Replaced the float with the nitrophyl one from Greg Lange.(2 years ago).  Lapped and trued the seat to get a good seal with a viton needle. ( I was afraid I would do major damage trying to remove the seat so I had to make a pilot lap to carefully true up the egg shaped seat.  Then resetting the float height.  I had to make a cage so the needle will find center and it appears to be working. I have checked to see that the vacuum tank is not allowing fuel to enter the vacuum line to the manifold. I may have to try Mark Shaw's suggestion about a cracked jet. One of the problems with the T series carbs is that the idle and high speed jets are unremovable. Soldered in place.  Trying to block internal passages to check for leaks will be a trial.

 So yes, Done all that and still not running well. Interesting that even though all the heat access has been blocked and the exhaust manifold control rod has been disconnected. When I move the heat control on the dash the engine speed changes. There should be no air control from the valve it is to operate. It is blocked in front and above to the heat riser.?????

[carbking]

I am NOT a huge fan of Marvel carburetors

 

That being said, a few tidbits that may (or may not) be helpful to those that wish to attempt to use them:

 

(1) The carbs built in the period circa 1925 ~ 1933 used a zinc alloy diecast that did not stand the test of time (Marvel isn't the only company to have this issue). Just be aware that the castings in this era can do all kinds of nasty tricks.

 

(2) The airvalve spring. Marvel used several different airvalve springs. MOST (but not all) have a free length of 1.5 inches. There are different "bumps" in the center (on some, some have no bumps) and different wire size to have a different tension on the airvalve. It is critical to use the correct spring. These are available in the better rebuilding kits.

 

(3) The "spacer block" (low speed venturi) is made from the aforementioned zinc alloy, and it tends to "grow". This destroys the design clearance between the spacer block and the lower edge of the airvalve. This clearance will effect the idle (and there are different settings for different Marvels). Once you know the correct clearance for your specific carburetor, the flat edge of the spacer block may be "sanded" on a flat piece of glass using 1200 grit emery.

 

(4) As mentioned by others in this thread, the cork float. The original floats were coated with orange shellac. Modern fuel, with or without ethanol, will cut orange shellac like a hot knife cuts butter. Other sealers should be used. Two that work are (A) POR-15, and (B) the model airplane dope used to coat the fabric on model airplanes, available from a model airplane shop. Most modern cork is "composite". Not only is it heavier than natural cork, the binder often is not compatible with modern fuel. We make float from the closed-cellular poly-nitraphyll foam; but balsa wood may also be used. Just make sure you coat the material AFTER the float arm has been affixed to the pontoon.

 

(5) The earlier floats have a cast brass arm affixed to the float. Bending on the brass arm is a sure way to get experience machining a new arm! Adjust the float, thus the fuel height, by using different thickness washers under the needle seat.

 

(6) Also mentioned by others is the propensity of the tiny brass jets to crack. More accurately, generally it is the long jet standpipe that cracks. The jet is the end, maybe 3/8 inch long, screwed into the top of the standpipe. These can sometimes, but not always, be soldered. If not, they are available, but since they must be custom made on a lathe, not inexpensive.

 

(7) The heat riser. Many Marvel carburetors use a heat riser system to heat the fuel to improve atomization of the fuel. With the volatility of modern fuel, this is generally no longer needed, even not desirable. Maybe in 50 below temperatures one still might need the heat riser. Probably best to block this off. Even totally blocked off, it is generally necessary to replace the insert tube in the heat riser. This gets lots of enthusiasts in trouble!!!!! The insert is pressed into the webbing of the heat riser (cast iron) which is quite fragile, and breaks easily. PLUS, most of the tubes are pressed into a blind hole, meaning they cannot be driven out. One takes the heat riser to a shop with a small boring bar, and the tube is bored until paper-thin and then can be removed. The insert tubes are weird sizes, and some are no longer available. We have a good selection, except sold out of those for Buick.

 

(8) The automatic design. This issue is not just an issue with Marvel, but plagues most, if not all of the early airvalve carburetors (Johnson, Schebler, etc.). The airvalve springs were designed for a fuel volatility that is simply NOT available today. Plus, if ethanol fuel must be used, the BTU content of the ethanol mixed fuel is less. This issue can make the automatic carburetors difficult to impossible to adjust. Yes, I know the knurled knob is an adjustment, but since the spring tension is now incorrect for the fuel, the adjustment is never perfect over the entire RPM range.

 

(9) The two different styles of fuel valves that may be in 1928 ~ 1930 carburetors. Some carburetors used both the articulated or the horseshoe and collar type. You have to specifiy which when ordering a rebuilding kit.

 

So if you want to rebuild your Marvel, maybe the above will help.

 

Jon.

 

[dibarlaw]

Jon:

 Thank you for your valuable insights. If you could recommend a bolt on replacement I am willing to try. Any updraft suggestions?  I truly dislike the flipped manifold look.

 No wonder these ads were around at the time.

[ROD W]

This is a 1920,  but the 25 is very similar.    You might have to file the air valve  a bit,  to get it to sit flush around the edge. There should be no gaps when closed. Check that the air valve pivot pin is not worn. and the air valve is moving freely and not sticking. 

[Hubert_25-25]

I have a 4 of these 1925 10-11 Marvel Carburetors.   All of the air valves stop short of closing against the carburetor wall.  They are short by roughly 3/16".  I say roughly, because they do not all stop in the same place.  Some 1/64 further than others.  They all stop short because the base of the air valve is laying against the semicircle block.  The air valve plates do not look like a lot of the exploded pot metal that I see on this vintage of car.  In picture 3, you can see the thin line of pot metal that I would need to sand on to make the air valve close.  I am a little reluctant to file or sand on this yet.  I can see where this should be a tight fit against the semicircle block when closed to prevent wear on the air valve itself.  I was actually waiting to see how it would perform "as is" before I attempted to sand on it.  I will say if this is a problem, it is very common, and would be something that needs checking and servicing at some frequency, as it means the air valve plate is changing and continues to grow over time.  Why does this sound weird? 

 

Please keep in mind that my car is not running, so I can not say what is correct.  I am only making an observation and looking for advise.  Thank you, Hugh

[carbking]

Hugh - for proper idle, the airvalve MUST close. The function of the spacer block is a "venturi" to accelerate the air stream past the idle jet to create sufficient negative pressure to improve the function of the idle. If the airvalve is not closed at idle, air will flow around the end of the airvalve, reducing the amount of air, thus the air velocity through the venturi, and past the idle jet.

 

While the sanding must be done ONCE on virtually all Marvels, it is not a recurring issue. Remember, it has taken 90 years for the spacer block to "grow" as far to its current condition.

 

Jon.

[Mark Shaw]

21 hours ago, Bob Engle said:

I would be careful on the wine cork float idea.  Many modern wine corks are made as a composite to assure better sealing.  These corks are a more dense material.  Restoration Specialty Supply sells a synthetic material that can be easily shaped.  This material eliminates any concerns about the float absorbing fuel.  

 

Bob Engle

Bob,

    Agreed, it must be real cork.

 

Larry,

    Zenith is a good replacement carb. & can be ordered by engine displacement via this website:

 

http://zenithfuelsystems.com/prod_carburetor.htm

 

Edited June 22, 2016 by Mark Shaw (see edit history)

[Hubert_25-25]

Jon,

Thanks for your posting and covering so many areas.  I will be sanding on my spacer blocks.  I thought this was so strange to see this on all my carburetors, but I also felt like they needed to close all the way, or would not function properly. 

 

Hugh

Edited June 22, 2016 by gr8success (see edit history)

[carbking]

Larry - SOME of the Marvels can be replaced more easily than others for a couple of reasons.

 

(1) Marvel used a proprietary flange on many of their carburetors. MOST other companies used either a straight flange or a cross flange mounting. Drawing a straight line through the mounting bolts of a straight flange carb would result in the line running from bumper to bumper if mounted on a vehicle. Drawing a straight line through the mounting bolts of a cross flange carb would result in the line running from fender to fender if mounted on the car. Many Marvels have an "antigoglen" flange. There are no replacement carburetors with this flange. Thus, a flange adapter must be fabricated.

 

(2) Because of the spacer block design blocking at least half of the throttle area, even Marvel straight flanges are larger than the straight flange for a conventional carburetor, so it MAY be necessary to fabricate a flange adapter even if the Marvel is a straight flange unit.

 

Using too large a carburetor (as is 2 above if no adapter was used) will cause the engine to run LEAN (insufficient venturi air velocity).

 

Also, modern carburetors are designed for pressure feed, while most of the updraft Marvels are designed for gravity feed. The new carb would REQUIRE MODIFICATION of the orifice in the fuel delivery system to accomodate the gravity feed.

 

So YES, it can be done, but often is not as easy, NOR as inexpensive as flipping the manifold.

 

Jon.

 

Edited June 22, 2016 by carbking (see edit history)

[1956cody]

Thanks to all who have commented/contributed to this topic. I am mulling over the various options and hope to do what is overall best for the car and its performance/originality.

Frank

[carbking]

Hugh - thank you for picturing the airvalve spring. I mentioned these in issue 2 of my first post. Your post jogged my memory that I had pictured several of these in the past. Here is a link showing a picture of several of the different Marvel airvalve springs:

 

 

Note that most are the same length (1.5 inches) but some are shorter.

 

Jon.

[Terry Wiegand]

I am going to have to side with Mark on this issue.  I am a huge fan of authenticity and having the original 'blasted Marvel' on the engine works for me.  Jon makes a perfectly good point in saying that these carburetors were not designed to run on this modern day crap that tries to pass for fuel.  I have had all three carburetors for my Buicks rebuilt professionally and the two that are operational seem to run really well.  Let me tell you the WHY of them running pretty darn well - I feed them 100% pure gasoline.  The last time that I had the '20 out and drove it it ran absolutely perfect.  It DID NOT belch, backfire, pop, cough, sputter, or stall.  For the 10 mile duration of the drive it ran just beautifully.  This is the original Marvel carburetor that the car left Flint with.  I am going to start using the pure gasoline in my John Deere lawnmower.  I ran one tankful through it and the engine was so much easier to start that it was almost unbelievable.  That's my story for now.

 

Terry Wiegand

A HOT Doo Dah! 

[Hubert_25-25]

Frank,

   I am learning a lot about these Marvel carburetors.  The venture is the semi circular piece of pot metal at the base of the air valve.  On all  my carbs, this has grown in size to prevent the air valve from closing all the way.  The first picture is a venturi from a 1926 Buick that has grown so much that the venturi hole is oblong.  It will only let the air valve close fractionally, so stuck almost wide open.  The second picture is the venturi from my 1925 Buick 10-11 carburetor.  You will need a good 5/16 flat head screwdriver to remove the 2 countersunk screws to get this out. (Do yourself a favor and use a new screwdriver to prevent messing up the head of the machine screw.)  Get a screwdriver with a square shank so you can put a wrench on it for leverage as these can be in very tight.  I did not see the cracks in the venturi until I removed it.  I plan to clean up the flat face and put this back in service. The clearance should be .009 to .017 between the base of the air valve and the flat side of the venturi when the air valve is against the far wall of the carburetor.     Hugh  

Edited June 24, 2016 by gr8success
was not able to download images (see edit history)

[Hubert_25-25]

I had to shave off a lot of metal to get the "tail clearance" correct between the air valve base and the venture semicircle.  The fine sandpaper on glass would take forever.  I used a medium to fine file, clamped it to a work surface and pushed the venture across it trying to keep it as smooth and flat as possible.   I think it did a fine job but it was still very slow.  The spec also calls out for the tail clearance to be .009 to .017, which is not only a huge gap to me, but also a pretty wide range.  So the first manner of business was to grind off enough to get the air valve to lay flat against the intake wall.  Then I started to actually get some tail clearance, but this is such a slow process, I quit when I had a nice even tail gap and just seeing an even light slit thru the gap.  Maybe about .005 tail gap.   Going to try it with this, because its hard to put the metal back on.  The venture is slightly oblong from the venture block growth too.  I will keep an eye on it and file it again in 10 years.  I think anyone with a Marvel carb should inspect this part if they are unsure of the condition.

Hugh

[Jim Bourque]

Hugh

looks like you have done a nice job on resizing the pot metal. Have you addressed the possibility of continued swelling/cracking? Or is the pot metal stable once it has swelled?

Jim B

[Hubert_25-25]

Jim, 

     My feeling is that the pot metal growth is slow, and the part is over 90 years old, but I would expect there could be continued swelling/cracking over time.  It is worse on some carburetors than others.  I have a reference point now to know how much it could grow in the future.  I have 4 carburators that started as identical parts, and now all the blocks are in various stages of swelling/cracking.  Not knowing the environments they were in, I can't judge, but maybe someone from Arizona still has a perfect one?  Theirs would make a great pattern to repour in a better metal.  Maybe someday it would be a good idea to put a coating material on this part to seal it.  But my car does not expect to be out in a lot of rain and humidity like the old days either.   Hugh  

 

 

Edited July 16, 2016 by gr8success
removed photos (see edit history)

[Hubert_25-25]

 

The 2nd half of this Marvel  book is a good reference for checking your carburetor set up.  The calibration chart that comes with it is handy.  Bobs Automobiia carries these, and I have seen them on Ebay.

Hugh

 

Edited July 16, 2016 by gr8success
rearrange order of photos (see edit history)