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#468141 - 11/30/07 08:28 AM
Marvel carb.
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Taco
Member
Registered: 09/11/07
Posts: 78
Loc: Netherlands
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Hello,
my Buick has a Marvel updraft carb, just like it has to be. 
As you can see at the photo above, the inside has some cracks.(seen at the bottom too) Is this a problem for using the carb?
So yes, where can i find a replacement? Is it repairable?
At this photo are two Nuts (screws) at the right. What for??
One is for the 'plunjer'.
At the last photo in the middle there is a 'plunjer' (not seen at the pic). What does it normaly??It wasn't connected to somewhat in the car.
What is step one for adjustment the hole lot?
Forgotten: It's a 1928 Opera coupe Master six.(posted somewhere else)
Best Wishes.
Taco.
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#468205 - 11/30/07 01:17 PM
Re: Marvel carb.
[Re: Taco]
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Buicksplus
Member
Registered: 09/03/02
Posts: 264
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Taco:
Those cracks in that flapper are probably no problem. You can safely repair them with JB Weld or similar epoxy. What is important is that the flapper valve moves smoothly and fits well to the throttle body when closed -- no sticking or major gaps.
The plunger you talk about is a needle that is lifted by a short linkage to the throttle -- it is sort of a power valve, designed to richen the mixture when the throttle opens. If you don't have this valve, I suggest you plug the jet in the bottom somehow or she may run too rich.
The two nuts are cleanouts below various jets in the bowl. Suggest you remove them and make sure the jets are clean and open. They are probably OK, your carb looks very clean.
The main mixture adjustments is the lower needle with that wheel on it. Begin with it by closing the valve, then opening it until the notch lines up with that post on the carb. The other adjustment is the air valve, controlled by that knurled knob on the throttle body. Open this knob so the end is flush with the brass spring clip that rides in the knurls.
If all the jets are open, close the choke and you can probably get the engine started. Marvels like to run rich, just crank open that lower valve and crank in the air valve if she needs more gas. You really have to get the car on the road to set the mixture right. Don't expect a super smooth idle with these Marvels, they sort of hunt about like a hit or miss tractor. If they are too lean the engine will run hot under load and she'll backfire a lot. If too rich, she won't rev up smartly and you'll get a lot of black smoke in the exhaust.
Hope this helps, Good luck and good Marvelling!
Bill.
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#468375 - 12/01/07 10:23 AM
Re: Marvel carb.
[Re: Buicksplus]
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Taco
Member
Registered: 09/11/07
Posts: 78
Loc: Netherlands
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The plunger you talk about is a needle that is lifted by a short linkage to the throttle -- it is sort of a power valve, designed to richen the mixture when the throttle opens. If you don't have this valve, I suggest you plug the jet in the bottom somehow or she may run too rich.
This is the one:
In my car it wasn't connected.
If i understand you correctly, i must connect it again.
Must the flapper normaly close completely?
In my case the flapper stays open 1/4 inch.
Taco.
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#468567 - 12/02/07 12:36 AM
Re: Marvel carb.
[Re: Taco]
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critterpainter
Member
Registered: 10/21/00
Posts: 599
Loc: Paso Robles CA
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The flapper must close completly for the engine speed to drop to an idle. If you can, remove the fixed piece and file or sand the face closest to the flapper until it will allow the flapper to close completely.
Bill
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#468851 - 12/02/07 10:54 PM
Re: Marvel carb.
[Re: critterpainter]
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Buicksplus
Member
Registered: 09/03/02
Posts: 264
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Taco:
Here is a picture showing how that linkage on the power valve connects to the throttle. There should be pin on the throttle crank just made for that linkage:
I note you're from the Netherlands. We had a nephew who lived in Eindhoven for several years. Loved it, but he is now back in the States.
Good luck and good driving.
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#468961 - 12/03/07 12:31 PM
Re: Marvel carb.
[Re: Taco]
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Buicksplus
Member
Registered: 09/03/02
Posts: 264
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Taco:
Most folks who drive these cars plug up the manifold heating system, all it does is enhance vapor lock. With today's volatile fuels, it is not needed. I also removed the butterfly valve in the main exhaust outlet on the front of the engine -- even when this valve is open, it restricts the exhaust and reduces power. I saved all the original parts, they can be put back for show if necessary.
If your car is backfiring, the mixture is probably way too lean. Open that needle valve on the bottom a half turn or more to richen the mixture.
Also if your air valve flapper is not closing completely, (as per your earlier post) that will also give you a lean mixture. See if you can get it to seat properly.
Bill, Albuquerque, NM
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#469425 - 12/05/07 03:51 AM
Re: Marvel carb.
[Re: Buicksplus]
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Taco
Member
Registered: 09/11/07
Posts: 78
Loc: Netherlands
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You are right.
I took another pic from my car, here it is:
In the middle you can see the pin that must be connect to the plunger.
Further i will plug up the heating system i think.
Thanks for the answers.
Taco.
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#469688 - 12/06/07 03:01 AM
Re: Marvel carb.
[Re: Taco]
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Fred Rawling
Member
Registered: 03/11/00
Posts: 733
Loc: Bellflower, Ca., Los Angeles C...
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Regarding the die cast piece in the venturi of the carb:
There should be a .005 to .003 clearance between the die cast piece and the flapper. If you do not have the clearance, the flapper will not close properly and the car will run but not as well if it closes.
The best bet is leave the die cast piece alone. If you try to remove it, it WILL break and there are no replacements available. I have one with cracks in it and it has lasted for over 84,000 miles that I put on the car.
Remove the flapper and with a piece of sand paper glued to a thin flat stick, sand down the face of the die cast piece. Re fit the flapper and check the clearance with the flapper closed. Do this until you have the proper clearance.
I did not go to the trouble of pluging the heat pipe from the manifold to the carburetor. I just set the valve in the exhaust open all the way and left the linkage to it on the shelf in the garage. I am in California with warmer wheather than you probably have and the car runs good.
As mentioned above, set the idle wheel with the notch one turn open to the post thatsticks down from the bottom of the carburetor. That spring on it looks like a good idea. I have had my valve stem work out and fortunatly fall on the splash apron where I found it when the smell of raw gas caused me to stop. I wired mine with a strand from stranded copper wire to keep it from unscrewing. Some carburetors had a clamp that attached to the wheel of the idle valve to keep it from working out.
Open the air valve so that the top is even with the end of the spring on the side of it. That lets the car start.
The valve on the bottom is for idle only. Set the carb to run using the air valve. Be sure that the car is well warmed up. Drive is around a bit. Then, I screw the air valve out until the car falters. Screw it back in counting the turns until the car picks up speed. Open the valve half the turns you just counted. From this point pull the accelerator rod back fast to rev up the engine. If it falters, richen the mixture (turn it in one or 2 turns and try it again). When the engine will rev up when you pull back the accelerator rod you have it set for good pick up when you start from a stand still. Also, if, from the middle point between stalling and acelerating, the engine does not falter when you pull back the accelerator rod, try one or 2 turn out on the air valve knob.
Fred
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#469709 - 12/06/07 08:24 AM
Re: Marvel carb.
[Re: Fred Rawling]
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Taco
Member
Registered: 09/11/07
Posts: 78
Loc: Netherlands
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Thanks a lot!
So, the brass pin see here at the bottom is my reference.
The notch has to be at the same spot as the brass post.
After all i was reading, it's the best that i took everything apart, to check if the flapper works alright.
Taco.
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#473483 - 12/21/07 07:40 AM
Re: Marvel carb.
[Re: Taco]
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Taco
Member
Registered: 09/11/07
Posts: 78
Loc: Netherlands
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The plunger does have a small hole in it, but why?
Taco.
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#479402 - 01/16/08 01:58 PM
Re: Marvel carb.
[Re: Taco]
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Taco
Member
Registered: 09/11/07
Posts: 78
Loc: Netherlands
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At this pic you can see the Air Valve isn't closed at all.
I have also an spare one (carb), and at this carb it's just the same.
BUT............
.....at all drawing (Master Parts Book)the Air Valve is closing completely.
I cannot find any 'adjustments' done later at my carbs.
How on earth is that possible?? 
Are they 'redone' at the factory?
Taco.
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#479785 - 01/17/08 06:12 PM
Re: Marvel carb.
[Re: Taco]
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carbking
Member
Registered: 11/26/04
Posts: 523
Loc: MO
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For the marvelous Marvel to work as well as possible (but never well) it is necessary for the airvalve to close. The culprit is normally the low speed venturi (the half-moon zinc-alloy piece) which is visible in your photo at the bottom of the airvalve.
The low speed venturi is constructed of a poor quality zinc alloy. With age, this zinc alloy "grows", wedging against the lower edge of the airvalve and preventing closure.
To repair, remove the two flat-headed screws affixing the low speed venturi in the throttle bore. Now carefully remove the low speed venturi.
Obtain a piece of glass, and some 800 grit emery paper. Place the emery paper on the glass, and "sand" the flat side of the low speed venturi, removing sufficient material to allow the airvalve to close (check often, do not remove too much material). From memory (we no longer work on Marvels), the installed clearance from the lower edge of the airvalve when closed to the low speed venturi should be approximately 0.005 inch.
Jon.
Edited by carbking (01/17/08 06:13 PM)
_________________________
Good carburetion is fuelish hot air!
Owner - The Carburetor Shop LLC (of Missouri)
The most expensive carburetor you will ever buy....is the wrong one for the application that you attempt to modify!
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#486196 - 02/10/08 11:16 AM
Re: Marvel carb.
[Re: carbking]
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Fred Rawling
Member
Registered: 03/11/00
Posts: 733
Loc: Bellflower, Ca., Los Angeles C...
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Jon,
I was always afraid that removing the screws from he die cast piece in the ventri would cause it to break. I always glued a piece of sand paper to a stick and sanded it down while it was still in the venturi.
What was your experience with them breaking?
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