1926 Buick Master 6 carb adjustment

[honeylocust5]

Hi all,

 

I recently started a 1926 Buick Master 6 after it had sat for 7-8 years. Before this recent start-up, I pulled the carb off, soaked it in carb dip, ran carb cleaner through all passages and reassembled. I set it per the instructions in a Dyke's book: air screw (big knob) parallel with the tang/spring and the gasoline screw (round knob with notch at bottom of carb) turned out 1.5 turns. The car runs well, but only at about 1/3 to 1/2 choke, even when warmed up, and in a very narrow range of choke engagement. It won't run at all with choke in, or out past 1/2. The puzzling part, and why I'm seeking advice is that adjusting these screws do... almost nothing. Slowly adjusting the gasoline screw in or out seems to have zero effect, same with air screw. The gasoline screw also has a very slow drip from it. Related?

 

Any help is greatly appreciated!

[ramair]

Perhaps the variable Venturi flap is binding, hopefully no one has replaced your original brass and steel carb with a 1928 pot metal one as these have a tendency to swell and bind.  I would look inside and make sure the flap moves and that there is minimal gap when flap is closed . Next thing to look at is the special double tapered spring under the big adjustment knob, sometimes these get stretch by previous owner or they get replaced with a spring from the hardware store, either way it will not work

[Mark Shaw]

1 hour ago, ramair said:

sometimes these get stretch by previous owner or they get replaced with a spring from the hardware store,

Check this first.  Float level is also critical...  Fuel leak can easily be solved by removing the valve and installing a new leather seal.  

 

 

 

 

 

Edited September 18, 2021 by Mark Shaw (see edit history)

[trini]

In my shop working days a common test by fellow mechanics is to spray some WD 40arround the manifold and carb while the engine is running. If there is vacuum leak the engine will speed up. If there is vacuum leak carburetor adjustment will be ineffective. 

[hidden_hunter]

14 hours ago, ramair said:

I would look inside and make sure the flap moves and that there is minimal gap when flap is closed

Our standard six had a lot of wear on the flat, it took a lot of effort to get it to sit properly again

 

We only need choke to start on sub 50 days 

[honeylocust5]

Mark, and all, thanks for the great info. Going to check this today. Dumb question - where do I find replacement leather for the gasoline screw seal? I searched for replacement packing and see many options, but not leather. Is one of the other types a viable substitute?

 

Thanks again!

[Mark Shaw]

It only takes two hole punches to make one.... 

I have a cheap set from Harbor Freight that works fine for making gaskets etc.

[Hubert_25-25]

See my carburetor rebuilding procedure.  I would bet your venturi has grown and it is not allowing the air valve to seat on the internal wall of the carburetor body.  When this starts to happen, the adjustments begin to stop working.   If you have a pot metal carburetor body, you will want to look for a replacement.  The gasoline needle is supposed to be loosened before adjusting the needle, then retightened after adjustment.  That makes the seal last longer and prevents stress on the adjuster hand wheel.  You can use leather to repack that seat, or 1/8 graphite packing that can be found at a hardware store.  You should also submit problems to the Buick Prewar forum if you want a faster response.

Hugh

 

 

Edited September 20, 2021 by Hubert_25-25 (see edit history)

[honeylocust5]

I pulled the carb off this afternoon and you (and others above) were right on. The venturi plate rests 1/4 inch off the throat of the body. Clearly some expanded potmetal. I am all too familiar with that problem but had no clue this was a thing in this particular instance. I can fix Bosch K-jet injection in my sleep but was utterly befuddled by a Marvel updraft! I snagged some faucet packing at the store too and am excited to see how it goes. I will follow your guide and report back shortly. Thanks again to all.

[honeylocust5]

As per the advice given upthread, I pulled the venturi plate out last night, spent maybe 5 minutes filing it. It took longer to remove the cotter pin and tap out the pivot rod than the actual repair. The main source of the binding was along the flat end of the plate, closest to where it pivoted on the rod - that edge demanded more filing than the curved lip of the plate. I repacked the gas needle, and installed the carb this morning. The car started effortlessly. After it warmed up, I dialed in the gas and air knobs and each were less than 1/2 turn from the base setting to get the car idling smoothly with no choke. Incredible - what a difference. Thanks to everyone who offered advice and the detailed rebuild guidance.

Edited September 27, 2021 by honeylocust5 (see edit history)

[Hubert_25-25]

You fixed the problem, but it reads as if the filing was on the base of the air valve.    Per the instructions, what should be removed are the 2 screws that hold in the air block (which has the venturi hole) in it.  Either way you can remove enough material to allow the air valve to lay flat on the carburetor body wall, but the air block will continue to grow.  That is why the suggestion is to buy a replacement air block rather than doing a temporary fix of just filing the air block.  New venturi air blocks are shown below. 

The thing that I find strange is that I have never had to remove the cotter pin and pivot on the air valve.  I always just replace the air block.  Maybe a difference in metallurgy - like a higher grade of pot metal (as in Jumbo shrimp).  It is pretty amazing how these carburetors start to working so well after just a little filing.  I wonder too if this problem presented itself in the 30's or if it took 50 years to develop?    Glad that it is working for you.   Hugh