Dual venturi carb question ? ? ? ?

Posted by Alberta Mike on July 20, 2006 at 04:14:01 from (64.42.242.10):

I posted this over on the Case forum and didn't get too much action so I'll try here.

I took apart a Zenith carb from an early 40's model Case DC4 yesterday and this carb has two pot metal venturi's in the carb throat. The larger one is the standard type that you'd see on most carbs, it simply drops into the carb casting and is held in place there, while the smaller (inner) one is supported inside the larger (outer) venturi. It is suspended there in place on a pair of arms that radiate out from the inner venturi. The inner one seems to "hang" in a couple of slots in the outer venturi casting. The inner one is not fastened tight when in position, it just sits in these slots and it can move (swing or wobble) which I'm sure is incorrect. You can see wear spots in the ends of the supporting arms and also in the slots in the larger venturi. When assembled in the carb, the smaller inner venturi positions itself so that the main (power) fuel nozzle (which angles up from the bottom) points itself into the center of the small venturi. I've seen a parts book that shows it to be one assembly although you can't tell if it is two separate parts. Here are some questions, maybe somone can help me.

1. Should this inner venturi be stable (tight and not wobbling) when in place? If so, I was thinking of trying JB weld to secure it since those venturi castings are pot metal. Or, any other suggestions?

2. Can anyone explain to me how this was originally kept in place rigidly in that assembly (or perhaps it is supposed to be one piece)?

3. What is the purpose of this dual venturi setup, I've never seen it before?

4. The smaller venturi can be installed either end up (as it is now loose and can be reinstalled in either direction). One end is a bit constricted compared to the other. Which end is up (towards the engine), the small or large opening end?

Anyways, lots of questions and so far no answers. Hopefully someone out there can shed some light on this for me, thanks for your help.

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