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Putting a Downdraft Carb on a 1931 Buick


SteveHotRod

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Hi,

I have a 1931 Buick Model 57 that had problems with the Marvel carb. After rebuilding it, I finally gave up and am in the process of flipping the intake manifold. I got a 2 BBL adapter for it and made spacers for the front and rear bolts so the cup washers will fit flush.

I'm thinking of using a WCD carb or an old Ford 2 BBL carb. Any thoughts here?

I did not completely take off the exhaust manifold. The gaskets are copper. I ordered new gaskets from Bob's Automobilia but they are fiber type(not copper) so I'm tempted to reuse the old ones which seem to be relatively new? Should I lube them? And lube the cup washers?

The 1931 Spec & Adjustments book does not seem to contain torque specs or order. Anyone have this info?

Thanks much for your help!

Steve<!-- google_ad_section_end -->

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Steve,

Frankly, I am a little surprised you decided to flip your manifold before checking this forum for other options.... Or, at least I didn't see that you did....

Did you check the steel tube inside the the heat riser casting for holes that may be allowing exhaust into the intake?

Did you set the float level just below the lower jet?

Did you spray WD-40 or starter fluid around the intake connections while running to check for leaks?

I am not suggesting that you shouldn't flip your maniford. Many have done it because they couldn't find the correct Marvel carb or they wanted better performance. I just don't think you to do it before you try other options....

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Hi Mark,

I did try some other things including rebuilding the Marvel, creating a new float from the Volare epoxy foam material, and setting the float about 3/32" below the lowest jet. All I'd do was get a gas leak out of the Marvel when I cranked the engine and no/little gas to the engine. (It would not start.)

The engine started easy with starting fluid & I could run it fine by pouring some gas into the manifold through the wiper vacuum fitting. So, after speaking to some other folks and doing some reading, I decided to flip the manifold!

Any advice/answer to my previous questions would be appreciated!

Thanks much!

Steve

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Steve,

I suspect your heat riser tube is leaking exhaust into the mixture.... This is absolutely the most common problem with old Buicks. The moisture from initial combustion creates water vapor that condenses inside the heat riser and rusts out the thin steel tube that separates the fuel/air mix from the exhaust. This happens on short runs that do not fully heat the system to evaporate all the water (like when you test run it in your shop).

In addition to the three items previously listed, check the jets for small cracks. Remove each jet and blow into it with your finger on the end to find leaks. If you find one is cracked, simply solder it and run a drill down it to resize the opening. These are very simple carburators and should be fixable as long as the castings are intact.

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Hi Mark,

Thanks for the info! I don't think that the pipe is rusted out. I bought the car about 2 years ago and it looks like someone went through the engine really well.

I also checked the jets when I rebuilt the carb. I agree that it's a very simple carb -- but I had a national old carb rebuilder tell me that he won't touch a Marvel as they are such junk!

So I've flipped the intake, made spacers for the front & rear manifold studs, got a longer front stud, bought & fabricated a carb adapter & I'm back to the questions that I posted.

Any additional info will be very much appreciated!

Thanks much!

Steve

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Too bad you couldn't get the Marvel to work. Most people have success wuth them if they are meticulous in cleaning, float setting and checking for cracks in the jet tubes.

Yes you want to lube the copper gasket. I tighten from center out. I only tighten the studs snug.Once the engine is running, I check for exhaust or vaccum leaks and tighten only enough to stop any leaks. Too tight causes cracked manifolds.

By the way, Marvel carbs had such a good reputation that they were the carb of choice on airplanes in the 20' and early 30"s.

Bob

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Too bad you couldn't get the Marvel to work. Most people have success wuth them if they are meticulous in cleaning, float setting and checking for cracks in the jet tubes.

Yes you want to lube the copper gasket. I tighten from center out. I only tighten the studs snug.Once the engine is running, I check for exhaust or vaccum leaks and tighten only enough to stop any leaks. Too tight causes cracked manifolds.

By the way, Marvel carbs had such a good reputation that they were the carb of choice on airplanes in the 20' and early 30"s.

Bob

In 50 years of working on carburetors, this is the first I have heard of Marvel producing an aircraft carburetor!

After Marvel (and several other small carburetor companies) was purchased by Borg-Warner; a new name Marvel-Schebler appeared. This company produced quite a few models of tractor carbs, as well as the MA series of aircraft carburetors beginning in the mid-1930's. However, this was NOT a Marvel design. The MA design was more similar to the TSX tractor design than to any of the earlier Marvel automotive designs.

Jon.

Edited by carbking (see edit history)
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Guest outlaw car man

Mark,

I agree here. I 've had you, Bob E., Pete, Paul and others help out with my various situations on my 1933 90s.

I just removed the Marvel from my black 90 and basically cleaned and reset it to factory specs. Runs just great. I was having some backfire issues, I believe gunk had built up a bit on the low idle jets causing the problems. Not anymore.

I rebuilt the Marvel on the green 90 , sweated the jets on, all that, and set to factory specs and mounted on the black 90, it to runs just great.

Took a lot of time and a LOT of patience and a lot of emails & calls to my Buick friends and it worked for me.

I like to keep em as stock as possible, that's my thing anyway.

I drive the black 90 about once a week to get the plugs and all heated up to temp, 5 -10 miles or so. Just love it.

Sandy

Frankly, I am a little surprised you decided to flip your manifold before checking this forum for other options.... Or, at least I didn't see that you did....

Did you check the steel tube inside the the heat riser casting for holes that may be allowing exhaust into the intake?

Did you set the float level just below the lower jet?

Did you spray WD-40 or starter fluid around the intake connections while running to check for leaks?

I am not suggesting that you shouldn't flip your maniford. Many have done it because they couldn't find the correct Marvel carb or they wanted better performance. I just don't think you to do it before you try other options....

post-54015-143138311499_thumb.jpg

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  • 3 years later...

I have a '31 Buick 8 L90 with an incorrect model Marvel updraft carburettor fitted, after hours spent checking and adjusting I just can't get the engine to run smoothly (running too rich). Also with gas at around 7 dollars a gallon in the UK I want to flip the manifold and fit a more economical downdraft.

Can anyone advise me what carburettor would work?

Would I bolt it direct to the manifold and dispense with the heat riser? as I can't think it would otherwise clear under the hood.

Any helpful advice would be much appreciated.

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  • 6 years later...

I did a conversion on my 32 Series 57.   I wrote up some of the process I followed.  Perhaps you might find something useful.   In the end I ended up using #45 or #46 jets.  Can't remember now.   So far no issues and love the quick startups.  A couple of pumps,  pull choke hit the starter and instant starting.

 

 

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On 2/26/2021 at 10:15 AM, A.A.Ron said:

Steve, do you recall what adapter you used for the down draft? I have a 31 series that I am looking to do the same flip as well as a few other upgrades.

I made one out of a piece of steel. I drill a hole that was size of intake manifold. Used a 40 Chev carb with bigger opening. So used a larger drill and make a taper. I can email a drawing.

Steve

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