1931 Buick 345ci vacuum question

[tcslr]

This is the big eight cylinder.  The engine was done by a very reputable engine shop.  I bought this car and am sorting it out.  Clearly, I have carburetor work.

The car starts beautifully - a bit of choke and off to the races.

 

The vacuum - once it warms up - I assume that is the proper procedure - I get a 'light' 17 in. ( it is a fine scale) say a solid 16-16.5.  very steady.  It does not fluctuate.  when I bump throttle, it coughs (yes  - carburetor work ( Marvel)) and drops to 6-7ish? maybe 5? then rises back to 18ish and slowly drifts in about 3-5seconds to 16-17.  

 

I borrowed this gauge - it has graduations and the needle is right between late timing and good ( I would much prefer high accuracy and then go from high fidelity data). Anyway, if anything, very slightly moreso in late timing.

 

I would like next step suggestions for diagnostics and testing.

 

FWIW, I like this Marvel - it is a simple thing and I believe I can get this properly sorted.

 

TIA and Merry Christmas.

 

Tom

[61polara]

Your vacuum values seem normal but low to me.  The drop when you bump the throttle is normal because you have injected more air to be pulled out by the vacuum of the system.  You should be seeking vacuum of as close to 20-21".  Tuning in the carburetor should get you there.

Edited December 25, 2021 by 61polara (see edit history)

[pmhowe]

I agree. It is normal, but low. I would check all the inlet and carburetor nuts for tightness. That has fixed the problem for me in the past.

Phil

[61polara]

You will also find that your vacuum wipers work much better the closer to 21" the vacuum gauge reads.

[tcslr]

Thanks.  That makes sense.  

[Hubert_25-25]

Decent vacuum, but not quite where it needs to be.  I would bet your pot metal Marvel carburetor venturi is likely the culprit.  I have placed my Marvel rebuilding instructions on the brass buick website.  There is information on where to order a replacement venturi and other parts.  These venturi's grow and will not let the air valve close all the way.  Air bypasses between the air valve and the carburetor wall at idle.   This prevents full vacuum from being achieved.  This photo shows a venturi that has grown and made the air valve completely inoperable.  The listing attached shows the venturi used in each model Buick.   

 

Use this link.  You likely will have to create a username and password.    

 

https://brassbuicks.groups.io/g/PBR/files

 

Look in the files section.  There is a file called "Carburetor-Marvel-rebuilding.pptx".  There are numerous repairs that need to be made to a Marvel Carburetor to get them back in operating condition.  

 

You should also ask your questions on the Buick Pre War Website.

 

Hugh

Edited December 26, 2021 by Hubert_25-25 (see edit history)

[Mark Shaw]

I suggest you first spray a little WD40 or starting fluid around the vacuum connections to find any leaks before rebuilding your carb.

Do the easy stuff first!

[Str8-8-Dave]

21 hours ago, Hubert_25-25 said:

Use this link.  You likely will have to create a username and password.    

 

https://brassbuicks.groups.io/g/PBR/files

Hi Hugh;  Is the "create password" link automated or do you have to approve application for membership to your group?  Numerous attempts to get a login link sent to my e-mail address have not resulted in receipt of a link.

 

Thanks.

 

Dave

 

[Hubert_25-25]

Dave,

    Gaining access to the brass buick and their prewar website may be delayed due to the holidays??  Someone has to grant that access.  Maybe Mark Shaw knows because he directed me to that website originally.  I have several files that I have placed there because they allow excel, word, and powerpoint formats.  This website only allows .jpg so in order to post stuff here, I have to snapshot each page of a technical document and then store that in another file.  Then if I have an update, I have to snap shot each page and store it again.   Keep us posted if you do not get in after the holidays.     Hugh 

[tcslr]

I have applied and need to be approved. I will try the WD40 also. The float lever on this carb is the early stamped part. I am going to swap out the lever to the later style. Thanks for the input. I am determined to get this operating perfectly. 

[Str8-8-Dave]

4 hours ago, Hubert_25-25 said:

Keep us posted if you do not get in after the holidays.     Hugh

I did apply so we will see what happens.  I'm interested in the venturi blocks and any tuning info you posted there and have a friend whose Marvel venturi blocks are a mess and he is considering casting them in some high quality aluminum alloy.  

 

Enjoy the rest of your holiday...

Dave

[Hubert_25-25]

Dave and Thomas, 

    In case you want to see the rebuilding file that I posted on the brass buicks website, I have attached another link here as I have posted my tech paper on this AACA website where I can keep up with the edits.  Plan B is to eventually post these on a google drive, but I am not there yet.   

 

https://forums.aaca.org/topic/372573-1920s-buick-marvel-carburetor-rebuilding/#comment-2311177

 

Note 2, Roger McGinnis and Tony Bult also have made several of the venturi blocks and have them for sale at reasonable prices.  My chart lists the blocks used for 1925 thru 1932.  If you talk to Tony or Roger, can you update me on who has which venturi blocks.   I believe Roger has 111-2, 111-4, and I think 111-8 is the same as 111-4.  I thought Tony had 111-3 and he may have others.  

 

Happy Holidays,

Hugh

Edited December 27, 2021 by Hubert_25-25 (see edit history)

[tcslr]

Wow. Impressive. I sent two PMs. I’d like to get your deck and the spring study. I did some measurements of the standard kit springs and calculated a spring constant but …. Any ideas where I might find an original spring?

Tom