Is this a Holley carb?
Anthony, this is a Kingston L4 I think.
I should have some photos of this somewhere
Here are a few photos taken during a rebuild.
Does this carb run better or worse than a Holley?
What does the extra throat valve do?
Mine is working well.
Other says different but ...
Here is Martin Vowell's drawing
I will try to explain the reason of the extra throat valve. I hope others will come by and complete my story.
First you must take in mind that the gasoline in the twenties did not vaporise as it does at this days and was much heavier.
On Dan's drawing you can see that the gas and the air comes together at the spray needle place. To get a good explosion you need to mix the air and gas very well if you do not, some of the gas will not burn.
As the gas was heavy at that time it was hard to mix with the air.
Look at the form of the valve, it looks like a spoon that is mounted upside down in the carburetor. By doing this the air and gas that pass the "SPOON" will turbulence more as in a straight stream and the gas and air will mix better.
The air/gas mix is more constant. You should have a more efficient explosion in the engine and you should get a better gas/ miles performance.
This is how I understood the reason of this valve.
My experience with the "spoons" is you should allow it to open as wide as it could go, there for you should cut the cork, that block the valve, as short as possible. For me the cork is only there to stop the clapper noise the valve makes as it open.
The L4 is very easy to build and very reliable. A friend has one that has had one rebuild in 50 years. May not be the most efficient or give the most power but who drives a T for gas mileage anyway? All I run so I guess I am biased. KGB
There was a dyno test in one of the T club magazines recently comparing various stock T carburetors on the same engine. The Kinston L series carburetors like yours were down about 20% in terms of torque and horsepower compared to a Holley NH. About the same as running a Holley NH with one of the plug wires removed.
Unlike the NH type carb the air does not pass right over the puddle of fuel on it's way to the engine. It enters then dips down into the fuel bowl then ether has to travel up the low speed tube or through the flapper passage as needed. In a Kingston L4 the area around the spray needle at the bottom rear of the passage is larger then the needle, at idle the fuel is pulled up through that passage from the puddle (low speed tube in the illustration), the flapper is closed at idle. As the need for speed increases more air/fuel is needed and the flap is pulled open by the suction and pressure of incoming air. The air then passed directly over the puddle of fuel into the engine thru the flapper opening bi-passing the low speed tube. The Kingston carb shown above is an L or L2 and shows the air flow at speed. There are some differences in the flapper bumper and flapper but are essentially the same in operation.
I have found that while true the L4 does not have the quick top speed of other carbs it is a good reliable carb that is easy to use and has a great low idle speed. It is one of my stable of 3 carbs, Stromberg L-1/Zenith intake (on the car now, needed to play and way more top speed)with Marvel straight though (mileage a bit lower then the Stromberg but not a bad carb)and L4 as backups.
Thanks for all the great info.
I picked up a N.O.S. brass L4 a while ago and have used it on my 14. I have the holly G on it now, and have also used an NH. I can not say I have noticed a lot of difference between them except the G gives me the worst gas mileage, about 15mpg. I got lucky with the G as it had virtually no wear when I bought it. I am only interested in driving 35-40, so maybe that is why I haven't noticed a big difference.
I have a Case 12-20 crossmotor tractor and it has a Kingston L-3 carb that has this valve also. It is a kerosene motor. Beside being an updraft, it looks the same inside. This carb design works good on low quality fuel. PK