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Single Choke vs Double Choke  Rating:  Rating
 Posted: 09-21-2005 04:54 pm
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1st Post

Joined: 08-05-2005
Location: Canton, Ohio USA
Posts: 73
My JH has two Stromberg Carbs. I see that just one has a choke cable connection. Can someone explain this choke system? I understand that there is some sort of hose between the two carbs that provides the choke to the other carb. I think this is the hose on my JH that is cracked (broken). Any detail information this system would be appreciated.

Last edited on 09-21-2005 04:54 pm by Jay

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 Posted: 09-21-2005 07:59 pm
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2nd Post
Mark Rosenbaum

Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532
Mounted to the front Stromberg is the 'start enrichment valve' that's usually called a choke.  A tube in this carb's float bowl connects the fuel in the bowl to the inlet port of a hollow disk having, as outlets, two matched sets of holes arranged from small to large.  These outlets feed passages connecting to the venturis of the carburetors, directly for the front carb, and via the hose you mention, for the rear carb.  One-way 'poppet' valves are also present to reduce the fire risk should the engine backfire.

Air flow through each carburetor results in a low pressure at the venturis, and the ambient pressure forces some fuel from the float bowl into the tube, through the holes in the disk, and thence to the two venturis.  The holes are arranged in size and position so that the amount of fuel provided increases with increased rotation of the disk.  And disk rotation, of course, is determined by how far the driver pulls the 'choke' knob.

The primary advantage of this system is that it provides a 'choke' function without needing any structure in the carburetor that would restrict or disturb smooth air flow.  There is very little that can go wrong, provided the valve was assembled correctly when the carbs were last rebuilt.

I've attached an annotated photo showing an assembled and disassembled 'choke'.  There's also a sort of schematic for Stromberg carbs at the start of this topic category (scroll down to the very end), that may be of interest. 
Addendum: It occurs to me that the annotations aren't as clear as they might be.  Specifically, the 'tube' in the photo is not the tube mentioned as leading to the fuel in the float bowl, rather it's the connecting point for the hose leading to the second carb.

Attachment: choke parts.jpg (Downloaded 77 times)

Last edited on 09-22-2005 03:24 pm by Mark Rosenbaum

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