Marvel Carburetor Disection

[Jeff in BC]

I'll be disassembling what I believe is an early carburetor using the following as references:

- Marvel-Schebler TXS - DTXS Service Manual (1952) http://www.oldcarmanualproject.com/manuals/Carbs/Marvel-Schebler/MS-DLTX-TSX.pdf
- Patent 1536043 (1928) http://www.freepatentsonline.com/1536043.html

I hope to be able to probe and follow all passages through the carb and compare them to the service manual and patent.

Components on the photos will be numbered with the same system as used in the Service Manual. This will allow the use of some of the diagrams in the manual; I will also use Marvel's terminology. Photos on the site are at a reduced resolution, if anyone would like full sized copies please PM me with your request.

Now on to the carb.

The Float System

Photo 1 - Float system with components identified:
1 - Float Bowl
2 - Float
3 - Float Valve
4 - Float Valve Seat
6A - Gas Inlet Model A
6B - Gas Inlet Model B
7 - Float Bowl Vent
8 - Float Valve Drain

Note - Fuel entry fitting is shown at the Model A position (6A). This may be moved to position 6B for use on a Model B.
Troubleshooting note: If you believe you have a fuel flow problem, the plug at the unused gas inlet (6B on above carb) may be removed to check for good gas flow. This is better than removing the gas line as it doesn't disturb anything in the system.

Photo 2 - Fuel inlet fitting/filter

Photo 3 - Close up of float and float valve and seat (valve open)
2 - Float
3 - Float Valve
4 - Float Valve Seat

Photo 4 - Top half of carb with all float components removed and fuel passages shown.
2 - Float (and hinge rod)
3 - Float Valve
4 - Float Valve Seat (and gasket above)
6A - Gas Inlet Passage for Model A (green wire)
6B - Gas Inlet Passage for Model B (white/green wire)
7 - Fuel Bowl Vent Passage (blue wire)

Photo 5 - Diagram from Service Manual

The above diagram is on page 2 of the Service Manual along with a full description of operation.

Photo 6 - Measuring float level

Service Note: Setting float height, the float should be parallel to the upper gasket surface. I used the float seam to gasket surface (15/16"). In the photo it looks a little off but this is camera distortion. If measured as shown the clearance between the gasket surface and the top of the float is 1/4". The height from the gasket surface to the bottom of the float is 1 3/4".

Photo 7 - Measuring the fuel level

I measured the gas level using witness marks in the fuel bowl. This distance is ~11/16" from the gasket surface to the marks in the bowl.

All for now
Jeff

 

[Joe K]

Gosh. VERY nicely done. And the witness marks are as plain as can be.

Is the needle on the gas float valve (item 3) anything special? Like a buna-N or viton tip or anything. Or maybe signs of being ground to a seat? Maybe you can take up the details of the float valve at a later session?

Joe K

 

[BudP]

Quite instructive and your presentation is very impressive. As this thread continues I will print out your posts and pictures and put them into my carburetor files for future reference. Thank you!

 

[crownfiretruck]

can you buy rebuild kit for these carb?

 

[Joe K]

can you buy rebuild kit for these carb?

SOME parts are available at Renner's Corner. See http://www.rennerscorner.com/carburetor.html about 3/4 way down the page. Pix below

$56 plus shipping for all above.

Some of the parts vendors have gasket sets. Tams gets $1.50 for the square gasket above.

Joe K

 

[leo]

Way to go Jeff, thanks for all your good work.

 

[leo]

Jeff, did you have problem backing out any of the screws from the metal body?

 

[jhowes]

Jeff; I have a version of this carb that you may be interested in, but I don't know how to PM anyone on this forum. How can I contact you?

 

[silversink]

Jeff; I have a version of this carb that you may be interested in, but I don't know how to PM anyone on this forum. How can I contact you?

Click on his name and click the private message that will appear

 

[Jeff in BC]

Hi All

Thanks for the comments. I'll try to answer all the questions.

Joe K - Here are some photos of the float valve and seat. The valve is steel or low grade stainless steel, it is magnetic. The threads on the seat are 3/8-27 UNS. The Zenith carb is 1/2-20 and the Tillotson is 7/16-24 so neither will work. I will try to find a replacement in the future.

Photo 1 - Valve, Valve Seat and Gasket

Photo 2 - Closed height of valve from gasket surface 0.1850" or approx. 3/16"

Leo - I did have some problems removing the float valve seat and the main jet do to previous attempts at disassembly. I had to very carefully use an impact driver.

Jack - Is the carb you have similar to the one in this thread post #5?
http://www.fordbarn.com/forum/showthread.php?p=879333#post879333

All for now
Jeff

 

[Joe K]

Heh. Valve needle the "old fashioned kind" that makes a metal on metal seal. Good for today's ethanol laden gasoline.

I see evidence that it may be either worn or ground to a seat.

Joe K

 

[jhowes]

The carb i have is identical in every way but has an different piece in the bowl. I have several marvel carbs and use them on my a. When i get moble again i will try to take a picture and post it but posting pictures is above my pay scale. Jack

 

[leo]

Jeff, should I assume that the three wires you displayed passing through the gas passage ways indicate there is no need to drill out any plugs to do a cleaning? There was no mention about the stationary gas jets? It appears the main jet is removable.

 

[Jeff in BC]

Hi All

I haven't forgotten about this project but a couple of things have come up that need my attention right now.

In the opening post I forgot to add that I will be going through the carburetor in four steps. So three to go.

Leo -
The first post was only the Float System, the next will be the Idle System.

From what I can see there should be no reason to remove any of the carb plugs during cleaning. The main jet is removable and should be removed before cleaning some of the other passages. I think this will become clear as we go along.

I'm hoping to get back to this over the weekend.

Jeff

 

[leo]

Jeff, you talked about using an impact driver to remove the float valve seat and main jet. Is this some type of small hand tool impact driver? Also, what if any parts would you not reuse besides the main gasket between the top and bottom of the carburetor?

 

[Jeff in BC]

Start of second post…

This is Part 2 of the carburetor dissection. I had second thoughts on how to break up the sections of the carb and decided to do the common paths separately. This means there will be a total of five parts to the dissection instead of four. Now on to the fun…

Fuel Bowl Drain System

When we left off last time the fuel bowl was full, we will now follow the fuel flow to the bowl drain.

Photo 1 – Drain system with components identified:
1 – Float Bowl
8 – Float Bowl Drain Plug
A – Fuel Cross Path (with lead plug removed)
B – Power Adjusting Needle (Gas Adjusting Valve, GAV)

Photo 2 – Fuel exit from the float bowl
18A – Power Adjusting Needle (GAV orifice)
18B – Power Adjusting Needle (fixed orifice)

Photo 3 – Close up of left path.

Note: The GAV can just be seen (bright vertical line) in the orifice.

Photo 4 – Close up of right path.

Note: The small fixed orifice is protected from sediment by the wall surrounding it.

Photo 5 – View of float bowl showing exit path for the fuel

I next removed the GAV (B) and the float bowl drain plug (8).

Photo 6 – Looking into the fuel cross path to the show path of the fixed orifice 18B

This is looking into the fuel cross path from where the lead plug was removed (A on Photo 1). I couldn’t get enough light down the path to show the green wire so I used a light beam to represent the wire. The light beam can be seen as the bright spot in the cross path about 1/3 of the way down. The threads at the bottom are where the drain plug screws in.

Photo 7 – Looking down hole where GAV has been removed to show the path of the GAV orifice 18A (blue wire)

Photo 8 - Looking into the fuel cross path to complete the path, 18A from the float bowl to the fuel cross path.

Photo 9 – Final path through the fuel cross path to the float bowl drain plug (white wire)

Behind the white wire the main jet orifice is visible.

Photo 10 – Side view of lower half of carb showing fuel level and fuel path through GAV

Here I balanced the GAV, with all its parts, on the side of the carburetor. The blue lines represent the fuel paths from the bowl through the GAV to the fuel cross path. The red line represents the fuel level in the float bowl. This shows that the fuel level is a little higher than the top GAV fitting. This is a possible source of leakage if the proper seals aren’t used during assembly of the GAV.

I see no reason at this point to remove the lead plug at the end of the fuel cross path during cleaning, All passages at this point are accessible and can be cleaned with carburetor spray cleaner and compressed air.

The next major post will be the Idle System.

All for now.
Jeff

 

[Jeff in BC]

Hi Leo

I'll try to answer your question.

Here's a photo of an impact driver, you insert screw driver bits or socket and then hit it with a ball peen hammer like a chisel. When hit the bit rotates slightly to loosen or tighten the fitting. If used on a screw it forces the bit into the slot so it won't slip easily. At the bottom of the picture you can see a couple of bits that have been twisted while removing screws, the screws weren't damaged.

The next picture is the driver in use.

As far as gaskets and seals go I would replace all of them. So far I have only shown the seal for the float valve and the bowl drain and the seal on the GAV but there is also the main gasket you mention and a couple of other seals.

Here is a simplified schematic of the fuel passages covered so far, it's a little rough but I will add to it as we go along.

I hope this answers your questions.
Jeff

 

[leo]

You are doing an excellent job and I again want to thank you for the great photos and detail your providing.

 

[jhowes]

Jeff; i appreciate all that you are doing here. Excellent job. The unusual carb that i have has something different where you show 18a in your presentation. When i am on my feet again i will check it out and try to show you what i am talking about. Jack

 

[Jeff in BC]

Hi All

This is part 3 of the carburetor dissection and is quite a long post. Actually too long, I’ve had to split this post in two (too many pictures).

The Idle System

When we left off last time we had fuel to the main jet and bowl drain plug so we will continue from there.

Photo 1 – Idle system with components identified:
10 – Idle Fuel Passage
11 – Idle Jet
13 – Idle Adjusting Needle

Photo 2 – Fuel entry to main jet, this is where we left off.

Now I will remove the Main Nozzle. The main jet, as shown above, is part of the main nozzle. Removal of the nozzle may be difficult and I would suggest using some of the following hints.

1 Make sure you use a good fitting screwdriver even if you have to grind one to fit. You can see the damage in the photo from using a poorly fitting screwdriver.

2 Clean the threads the best you can before attempting removal.

3 Soak the nozzle down with penetrating oil and let it sit then clean it out with carb cleaner. This should remove a lot of the junk. Now soak down one time with the penetrating oil and leave it there during removal.

4 The nozzle is a fairly tight fit in the carb body so be patient removing it, you may need to rotate it back and forth add more penetrating oil.

5 If the above doesn’t work or the slot is damaged you may need to carefully use an impact driver. I did.

Photo 3 – Main nozzle and seal.

The seal may be left behind in the passage where the nozzle was removed; it could be very hard to see.

Now back to the idle fuel path.

Photo 4 – Nozzle showing idle fuel path (green wire).

The red line represents the fuel level in the fuel bowl.

Photo 5 – Looking into fuel drain plug hole to show idle fuel passage (10).

Photo 6 – Side view of lower portion showing fuel path (green wire) from the drain plug to the idle jet (11).

Photo 7 – Side view showing idle well (10) entering the upper portion of the carb.

Notice the protrusion on the exterior just below the idle adjusting needle; this is for the idle tube.

The rest of the idle system is contained within the upper portion of the carb. I’ll break the post here and continue with the upper portion separately.

Jeff