Zenith carburetor for Harley JD

[MMasa]

Does anyone (Cotten?) have a sketch or measured drawing of the Venturi for the Zenith carb used on 1924,25,? Harley J models? I was going to make a run of them. They were originally pot metal and are always cracked and useless. I have some carbs that I could go through the effort of measuring myself, but I figured that I would ask first. Why reinvent he wheel.
Mark Masa

[T. Cotten]

Sorry Mark,

But nobody has trusted me with a Zenith yet.
(And I use an obsolete "digital" control for forming the 'airfoil' anyway: emery on my index digit.)

....Cotten

[MMasa]

I would use my CNC lathe to make it. Piece-O-Cake. I just need to know the form. If I know the length, minimum bore and the position of the main jet, is there a formula that I can use. Correct me if I'm wrong or if I'm over simplifying this, but it's just an airfoil form isn't it?
Mark

[T. Cotten]

Mark!

As I posted my, program would be useless for your CNC methods.

And honestly, many of the DLX Scheblers of similar vintage that I encounter require replacement venturies to be significantly over-length, in order to bridge over wear marks from venturies that were so loose that they rattled themselves into the body. The grooves are usually far deeper than even the throttledisc wear.
The throttledisc wear repair demands a larger body bore, so the venturi OD varies greatly as well, as no more than necessary should be removed.
Thus it is most practical for me to cut each venturi and disc 'one-off'.

The profile of the 'airfoil' should be very simple for your AutoCad (or whatever), once you have decided upon a length, OD, and bore.
Have you a fossil original of any sort? Certainly it was a nominal bore size.
The position of the main nozzle spigot (I assume it has one, perhaps another) is always just behind the tightest spot of the venturi bore.
I locate it by placing the nearly-finished venturi into the body, and then marking it through nozzle "well".

With no familiarity, I cannot imagine if there are constraints posed by idle circuit bleeds, or whatever.
Is there an annular chamber around its OD, for an "air correction circuit"?

None the less, if you intend to make a batch, I would suggest producing raw oversized blanks, lest they be "one-size-fits-none".
If they resemble DLX's, I could use many!

....Cotten

[MMasa]

Making them with an oversize OD is a great idea. Looks like I'm going to have to reverse engineer this one myself. Are there any standards with regard to the angle at the inlet and exhaust? I seem to remember reading something about the inlet side being 30 deg and the outlet being 5 deg.
Mark

[T. Cotten]

Mark!

I think airfoils are an infinite number of angles. Perhaps five and thirty were some sort of average.

With nobody standing over my shoulder to explain CAD programs, I never could "snap to it", but it seemed like you could bend a line from the OD to the bore, and then stretch it to just ahead of the nozzle hole, giving a cross-section like an aircraft wing.
The area of most "lift" to pull from the nozzle would be as ideal as any original I'm certain, and free of the artfull imperfections of my arthritic finger approach.
Then reproduce it inverted at the top of the venturi, and there is your cross-section of the bore.

I need 1.2" OD blanks, but from ebay pics I have snagged, I would guess the original Zenith body bore was more like 1 3/8". Photos of one broken down would be greatly appreciated!

....Cotten

[T. Cotten]

Mark!

If those Zenith's venturies are a nominal 1 3/16" OD, I'm ready for several.
There's a curious DLX76 overdue on my bench (everything on my bench is overdue), and I finally drilled my honing torqueplate for it, and measured. It is starting out a shocking 12 thou over by its own decades of distortion alone, and the original venturi cut much deeper grooves than the disc.
(Its even worse than most 113's!)

So either the 'blank' must be extremely over-length as well, or else the annular void around the outside must be cut under-length drastically.

Does the original Zenith venturi look anything like a Schebler?
Got 'macro' on your camera?

Thanks in advance,

....Cotten

[rwm]

these are not the best photos. the original venturi swells up and cracks. it wont just fall out. you need to hack it out in little bits. i'll try to dig out the new one i have. the new one is installed in a carb. it was made smaller on the inside diameter. this is the old one

[rwm]

[T. Cotten]

Mark!

Now I understand the difficulty of guessing the original dimensions!
It appears that it is unsupported for a portion of its length.

The un-exploaded section was so fused to the casting that I had to machine it out.
It cut quite "gummy", so I would imagine we have a real case of "lead-pest".

But the dinosaur throttledisc doesn't appear to cause much of a wear problem that would require re-sizing, so the oversize blank idea maybe pointless. (Whoops! Scratch that, another on my bench is indeed quite worn!)
Do H-Ds also use the T3½ body? (I now see by the literature that it is a completely different animal. What are JD's venturi bore?)
This original venturi's bore appears to be a tiny 5/8", with an overall length of 1½", fitting into a bore that starts out at 1.027";
I could use a handfull at 1.040" OD, if you still plan on making any.


.....Cotten

[MMasa]

Cotten
I wouldn't attempt it without at least a half decent sample to reverse engineer.
Mark