Steve Jelf sent me an actual Center Drain to work from, but I had to make some adjustments for the 1920-1925 version, because the one he sent me was a 1926-1927 model.
Looking through Bruce's parts list and encyclopedia I came across part number 6215, which is labeled "air vent". It's a small brass screw in vent that is supposed to go somewhere on or in the NH. But I couldn't find it anywhere on the one Steve sent me. I asked him if he's ever seen one and he informed me that all of the different NH's he's disassembled he's never seen one either. Which leads me to think that maybe this one of those little parts that didn't make into any of the production models of this carburetor, but for some reason didn't get scratched from the documentation either. I'm not sure what the story is, but that's what I'm going with at this moment.
Another peculiarity is that none of the small gaskets (adjustment needle clamp nut nor does the little staple looking wire that holds the throttle and choke plates to their shafts) and some hardware doesn't have part numbers associated with it. Not sure if these particular parts are used in previous carburetor builds (like the Holley H-1) and haven't changed since so there was no reason to assign a number to them or Bruce just didn't find any information on them when he was compiling his book. Doesn't really matter I guess, I just resorted to Lang's numbers for these parts, since that's where you're going to have to go to find them anyway.
The way to read the numbers is;
The bold number on top is the Ford Catalog number, the italicized number to the left of the comma are Ford Factory Numbers and the numbers to the right of the comma are the Dates they either appeared in Ford's catalog or the change dates, not quite sure on those, because in the column for "actually used on car" there is usually no date whatsoever.
Made a mistake, the short arms are on the 26-27 and the long arms are on the 1919-1924
Martin : Very nice drawings thank you.
one thing ; there is no gasket under 6208
Anthonie, according to the Holley parts list and Bruce's encyclopedia there is. But you may be right, it may be one of those things like that stupid screw in vent (6215) that just didn't make into the production run of this carburetor and was just not deleted for the documentation.
Martin, the air vent screw was only used on the straight thru NH carbs. these were only used around 20 or 21. The staple for the butterfly was changed to the butterfly having tabs punched thru them that expanded when the disk wad pushed thru the throttle and choke shaft.
And 25 was a transition year to the swivel fuel valve. (Late '25)
Jim, oh goodie that straight thru NH is on my machine now, at least I'll have a home for the little piece of brass.
So the throttle and choke plate changed to the tabs in 22? I'll make the change, just happen to have that drawing too.
Ken, Bruce's Parts List lists the part as 20-26. I knew it had to be somewhere around there, I just took a guess. Sooo, late 25 would be a 26 right? Like the two man top in 22, early in 22 it was a two man top, late in 22 it switched to a one man top with a slant windshield. Some folks say that's because it's an advance release for 23 and not a 22 at all (even though it was made in 22).
Ken Kopsky, how about the long arms on the throttle and the choke, did they also switch to the short arms around late 25 too?
Ok, here's the latest revisions...
1921 - 1922
1922- Early 1925
and 1925 - 1926
Just so there's no confusion, I'm talking about model years. My late '25 Touring is definitely a 1925 model year. It's from May or June, I forget at the moment. It has other features that were defined as being on a '26 model year such as the rear window, 2-rivet brake quadrant, side curtain mounts and rods and probably a few others. But it is a 1925 model.
I'll have to check the carb on the arms but I don't have one to compare so whether they are long or not will be a judgment call.