On September 28, 2013 @ 9:14 AM, Jim Mahaffrey made an interesting observation about the pictures in the book titled: Model T Ford Service Bulletin Essentials. On page 464 it appears that the drain valve assembly has a hole top to bottom. On page 470 is another picture that has the drain valve assembly that does not have the hole from top to bottom.
So that we are talking the same part, it is Factory # T6328E or Part # T6291. The parts books only list that one number, so I believe that only one style was used in the Holley Vaporizer. I believe the Page 470 picture is correct. The Ford service bulletin on page 123 (of the factory service bulletins) shows a good picture of the Vaporizer and it clearly shows a hole top to bottom for Part # T6291. I have no proof but I believe this to be in error! It has been mentioned on this forum before the one must use a drain valve assembly without the hole top to bottom for the Vaporizer to operate. It is unfortunate that the NH style drain valve screws in the vaporizer, and once installed, one cannot visually see the problem. Under operating conditions there is a restriction (jet) that restricts the flow of fuel to the intake manifold. If one uses the drain valve assembly with the hole top to bottom this jet does not restrict fuel flow and the Vaporizer will not work properly!
I've been looking closely now at every picture I can find of the Ford/Holley vaporizer cross section. No two are alike! It looks as though there were some changes.
The picture of the drain valve assembly on page 470 of Essentials may have simply been wrong. The purpose of the diagram is to draw your attention to the float height adjustment, and demonstrate that it was unchanged from the NH. I now think that the diagram shows an NH bowl.
However, the diagram on page 464 is quite strange, and it definitely shows a gasoline pathway independent of the needle valve. What's more, the vertical passageway to the air inlet is enlarged, making it a pool.
I checked my own example of a Ford vaporizer, and it physically corresponds to this diagram. Why purposefully drill a hole in the top of the drain valve it it wasn't functionally necessary?
There is a third type of diagram. It's in the Ford Instruction Manual This one shows the same configuration as page 464, BUT there's a metal disk atop the hole in the drain valve. This eliminates the drain valve as a gasoline source to the mixing chamber, while retaining the original part. Why they didn't just quit drilling the hole is not clear. They may have had thousands of them in inventory. Needle valve adjustment instructions are identical to the NH instructions. With the clear hole in the drain valve, there is no needle valve function.
In the diagram that shows a blocking plug on top of the drain valve (also seen in trade advertisements), the gas/air passageway is reduced in diameter.
Any help in figuring this out will be most appreciated.
The fact that only one number T6291, is listed makes me believe that Ford only made one part for the Vaporizer. Perhaps the illustrator used the NH part (T6221) in the drawing.
Perhaps Ford did use "blocking plug" at first, I do not know, but it would be less costly for Ford if he just did not drill the vertical hole completely through. He indeed did make the part with the vertical hole not drilled all the way through, as all the vaporizers I have seen did not have a vertical through hole in the drain valve body.
Perhaps others who have used or are familiar with Vaporizer carbs might want to comment.
Here are two older drain valves. The one on the right came out of my vaporizer. If there was a disk or some kind of plug it got lost when I took it apart. However the car was barely running when I got it so it may have missing then.
The question has to be asked: If Ford never used the configuration shown on page 464, then why drill the hole in the drain valve?
I do think that there was a quick change. The vaporizer strategy for the initial fuel/air mix, using heated air, may have been modified after a low number were sold using the machining shown on page 464. There was an interim period in which the solution was to block the hole with a simple slug and use the parts available. Later, the stems were built without the extra hole, and the need for the slug disappeared. I'm not sure why they didn't do away with the hole in the drain plug, unless their initial order covered a couple of years of anticipated production.
It's interesting to note that the first vaporizers were factory installed on some model-year 1925 cars. I wonder if anyone has such an installed vaporizer, or if they were quickly converted to NH? I notice that the first 1926 cars, as shown in the maintenance manual, had the Holley NH, as though the first vaporizers tried in 1925 were unsatisfactory.