Installing and Tuning the Stromberg B No 3 Carburetor on your Model T Ford

This is one of those times the short cut didn’t save any time………
The original steel rings were used with a new set of copper glands on the Stromberg intake manifold.

When we left off the Stromberg B No 3 carburetor was rebuilt and ready for installation. The installation turned out to be easy. Tuning was another matter! Read on to see what we had to do to get a sweet running Model T again.

We removed the old manifold and carburetor, using half clamps to keep the exhaust manifold in place so we only had to replace the copper glands on the intake. Installation of the intake manifold was simple.
With the intake in place we swapped the half clamps for whole ones.
With the intake in place we installed the intake / carburetor gasket and cinched the bolts down.
We had to fabricate another throttle rod from 3/16″ 4130 steel rod stock. We started at the carburetor end with the throttle butterfly closed. 
On the steering column end we made a mark with a Sharpie where the bend needed to be.
We bent it so the rod would certainly be too long. This allows us to add minor bends until it is perfect.
Drilling the cotter key holes starts with a center punch. 
Then a 3/32″ (#40 AWG) hole is drilled in each end.
December 1912 Stromberg advertisement for the new B series carburetor. The float being made of brass and the needle / seat shutoff in these carburetors is very well built and therefore unlikely to ever leak.
We start fabricating a temporary testing fuel line from 1/4″ OD copper tubing by placing a 90 degree bend as close to the end as possible.  
With a spare fuel inlet fitting we swage a ferrule on the end, then add a second 90 degree bend as close to the first one as possible. Then we twist the end with the ferrule so the end points upwards.
The line is temporarily installed so we can mark the cut off point at the shutoff valve end.

We install our fuel line and throttle control along with a choke rod. The gas was turned on. No leaks after five minutes! With the choke on and the ignition off, we pull the crank a couple times. Then we opened the choke and pulled another two quarter turns on the crank so that all four cylinders would hopefully be primed.

With the key on BAT and the throttle down a few notches, we pulled the crank upwards and were rewarded with an easy start! With the spark pulled down the key was switched to MAG. The engine was quite responsive but way too rich at less than 1/4 throttle. Hmmmmmm. Time to experiment with tuning.

With the engine running the float level can be adjusted by turning the adjuster. Clockwise = leaner mixture / lower float. We went as far as it would go and the mixture was still too rich. 
Literature supplied when the Stromberg carburetor was new dated April 1912. Our carburetor is Type B No 3 – 1 inch.
This type of carburetor has a brass float and very sturdy inlet needle / seat which should yield years of stellar service.

With the float adjusted as low as it would go, we tried the spring tension adjustment on the automatic air valve. Loosening the adjusters would decrease spring tension, allowing the valve to open earlier. With the adjustments both set to full lean, the carburetor was acting a little better but was still way too rich, particularly at idle.

The red arrow indicates the automatic air valve spring that came with the carburetor. The yellow arrow indicates the spring that eventually fixed our troubles.

We tried a succession of springs on the automatic air valve, each weaker than the one preceding it. Over the course of two days and several hours of work, the car ran better each time a weaker spring was installed, but was still too rich at idle. We finally went to the local Ace hardware store and looked through their drawers filled with dozens of different springs. We bought two promising candidates ($1.50 each) and cut them to length for testing.

This is the package for the spring that fixes the problem. We cut it to an overall length of 5/8″. By adjusting the lower spring tension upwards a bit the air valve would just stay closed with the engine off. 

With the new spring installed and the engine running, the difference was dramatic. The engine now accelerates crisply. Idle is dead smooth. We got 15 free starts in a row before the engine stopped in a spot where the ignition was not firing. Now we just need to go for a test drive.

Adjustment is accomplished (after the proper spring was found) by rotating the thumb nuts “A” and “B” for Low Speed and High Speed, respectively. We found that the low speed adjustment affects high speed, and vice – versa.

Out on the road, the car ran very well. Idle speed is quite low. The car has excellent response to throttle input. Cruising at low speeds or medium speeds is effortless. We went as fast as 40 MPH at one point to see how higher RPM’s would work. Very good manners at all road speeds.

We shut the car off and left it for a couple hours. Upon our return the throttle was opened about 1/4 of the way. The ignition was switched on. The car started on the first 1/4 turn of the crank.  It has more torque at any speed compared to any of the Ford supplied carburetors.

Another carburetor that performs quite well, and looks good too.

The Stromberg B No 3 had been sitting on a shelf in the garage for years. I was a little bit afraid to put it on the car due to it’s complex appearance and unusual design. We won’t make that mistake again!