1938 Buick Special Carburetor trouble

[Hubert_25-25]

1938 Buick Special Carburetor works great 98 % of the time.  When warmed up and then running at say 50 mph for 1/2 mile, then come to a stop light.  The car will idle fine for a little while, then the idle will begin to waver, and then the engine will die.  It does not want to restart.  Removing the air cleaner and look deep into the carburetor.  It looks like a 1/4" deep pool of gasoline is sitting above the thottle plates and the gas looks to be boiling.   It looks like gas is sitting on the throttle plate and not letting any air get thru and the car becomes choked and rich, and then dies.  If I let the car sit a few minutes, hold the pedal to the floor and crank it, it will eventually start after about a count to 15.  Then it runs fine.  I also tried just turning the electric fuel pump on and not starting the engine.  I do not see gas flowing into the carburetor so it does not seem like the fuel pump is overpressuring the needle and seat. 

     Another reason for asking about this is that I swapped this carburetor for another one that was doing this.  Is this a common problem with these original carburetors?  Any input is appreciated.  Thank you. Hugh   

 

[EmTee]

I wonder whether the fuel in the bowl gets hot, starts to boil and then the float is no longer buoyant enough to close the needle valve.  If so, then the engine floods.  Even after stalling, fuel may be siphoned into the carburetor until the fuel cools down.  I'd first check the float setting and the float itself.  If those check out as OK, I might try installing a heat shield under the carburetor.  If the fuel is boiling, I wonder whether adding a little kerosene (or diesel?) to the gas would raise the boiling point enough to help.  The octane reduction shouldn't be a problem for this engine.

[MCHinson]

Do you have an insulating base under the carburetor? I think that EmTee is probably correct. I have never experienced that problem but I have never operated a Buick of this era without an insulating base under the carburetor. I think they are needed with modern fuels, probably to prevent the problem that you are experiencing.

 

https://bobsautomobilia.com/shop/carburetor-items/carb-base-insulator-4-bolt-holes-1935-52-cbp-360/

 

https://bobsautomobilia.com/shop/carburetor-items/carb-base-insulator-3-hole-1934-40-cbp-350/ 

[Ben Bruce aka First Born]

Carbureted cars just do not like the gas that is formulated for pressured EFI systems. Precisely the reason my 1950 has no carburetor.

  When I would first notice/hear the condition you mention, I would simply increase the idle speed until it cleared up. If a long stop, might need to do so a couple times.

 

  I envy you that coupe.

 

  Ben

[nat]

     Nice looking car.

     Is the mainifold heat control valve working properly?

 

[EmTee]

When I park my car in the garage after a drive and open the hood I can literally hear a 'fizzing' noise coming from the carburetor...

[carbking]

The first thing I would check would be fuel pressure at the carburetor using a fuel pressure gauge.

 

Stromberg specified a maximum of 3 psi at idle.

 

Fuel level in the carburetor bowl is basically dependent on three things:

 

(1) The buoyancy of the float

(2) The diameter of the fuel seat orifice

(3) The incoming fuel pressure

 

It should be noted that under normal conditions, the float will not be completely covered with fuel. When the float is unable to shut off the fuel flow at normal settings, the fuel level will rise on the float somewhat increasing the float buoyancy.

 

In fewer words, it MIGHT be that the fuel level is TOO HIGH, but not sufficiently high as to run out of the carburetor. This could cause the carburetor to overfuel the engine at idle.

 

Thus, test number one would be actual gauge fuel pressure, not an index mark on a fuel pressure regulator (if one is being used).

 

If the pressure is less than 3 psi (2 1/2 would probably be better with the p/p being sold as gasoline today), then fuel pressure is probably not the culprit. In this case, I would try a phenolic spacer as others have mentioned in this thread.

 

All of the above is assuming you are using the original Stromberg carburetor. If you unfortunately have the Marvel, the ONLY suggestion I have is replace it with a Stromberg. I have not seen specifications for Marvel fuel pressure, but with the hokey float arrangement Marvel used, I would doubt much about 1 psi would work.

 

More on electric fuel pumps: Electric fuel pumps and older cars.

 

One quote from the article:  "Thus it is quite possible, if the wrong electric pump is chosen, to have a pump that floods the engine at idle, and has insufficient volume to maintain proper carburetor bowl level at wide open throttle."

 

 

 

 

[Oldtech]

I too am wondering if you heat riser is stuck shut putting excess heat on the intake.

[Hubert_25-25]

Thank you for all the input.  I do have the insulator block in place under the carburetor.  I plan to order the copper blanking plate that is available for the 248 engine.  Oddly it lists starting with 1939, but the 248 engine came out in 1937, so hoping this is just an error with the listing as the gasket set starts in 1937.

In the first photo, you will see the exhaust divertor valve counterweight and spring.  There is a spring hanging on it doing nothing.  I do not know the position of the valve as the car is not near me at this time.  First order of business is to see if the valve moves, and try driving the car with this set in either of the 2 positions. 

Wondering if this heat valve can be removed without removing the intake and or exhaust manifolds?   

 

[demco32]

On 9/29/2023 at 6:23 AM, Hubert_25-25 said:

1938 Buick Special Carburetor works great 98 % of the time.  When warmed up and then running at say 50 mph for 1/2 mile, then come to a stop light.  The car will idle fine for a little while, then the idle will begin to waver, and then the engine will die.  It does not want to restart.  Removing the air cleaner and look deep into the carburetor.  It looks like a 1/4" deep pool of gasoline is sitting above the thottle plates and the gas looks to be boiling.   It looks like gas is sitting on the throttle plate and not letting any air get thru and the car becomes choked and rich, and then dies.  If I let the car sit a few minutes, hold the pedal to the floor and crank it, it will eventually start after about a count to 15.  Then it runs fine.  I also tried just turning the electric fuel pump on and not starting the engine.  I do not see gas flowing into the carburetor so it does not seem like the fuel pump is overpressuring the needle and seat. 

     Another reason for asking about this is that I swapped this carburetor for another one that was doing this.  Is this a common problem with these original carburetors?  Any input is appreciated.  Thank you. Hugh   

 

I think it is the idle jet

[MCHinson]

If that exhaust diverter is not operating properly, it will certainly cause a problem, typically the car will overheat, so that could be the problem or part of the problem. You can't really "set" it in one of two positions. If it is moving, it will freely flap around unless the spring assembly is holding it. I never can remember from looking at the outside, which position the valve flap is pointed. With modern fuel, I actually think that removal of the diverter valve flap is a good idea. The reproductions of those sections's do not have the diverter valve flap. I am afraid that you are going to have to do some major disassembly to remove the flap.  

[EmTee]

22 hours ago, Hubert_25-25 said:

Wondering if this heat valve can be removed without removing the intake and or exhaust manifolds? 

I used some steel wire to lock the heat riser open on my '38.  It does slow warmup a little, but I prefer to be certain that the valve opens completely.

[nat]

9 hours ago, EmTee said:

I prefer to be certain that the valve opens completely.

     Open or closed?

[EmTee]

I wired it open.  @MCHinson tells me he believes he removed the flapper valve when he assembled the manifold, so maybe my modification isn't really necessary.  I'll check the state of the valve the next time I have the header pipe off the manifold.