When I first looked at the photos of that carburetor, I thought, “What the heck is that thing on the front that looks like a dash pot?” I looked again today and noticed that as you look down the throat, that’s no conventional choke. That’s a piston. I’ve never seen nor heard of a downdraft carb with a piston and a dash pot so I guess I might be excused for not seeing what was there in front of me.
Carbs with pistons go back to 1900 or 1905 depending upon whom you believe. They were invented by a Brit named Skinner and produced by his company Skinner’s Union or SU. I like to call them SU type carbs, but the Brits called them “Constant Depression” because they maintain a constant vacuum by means of a variable venturi. I have no explanation why they call a vacuum a “depression”. I checked a few websites for info about these carbs and Wikipedia claimed there were a handful of downdraft SU carbs used on cars before WWII.
I imagine Suzuki chose a downdraft carb to make it easier to service on a front wheel drive car and because they are familiar with the sidedraft type of this carb on motorcycles.
The piston retracts into the dash pot (a cylinder found on top of sidedraft SU type carbs and this varies the size of the venturi as well as the mixture by means of a tapered needle that sticks out of the bottom of the piston and into the main jet. In typical SU carbs, the main jet can move away from the piston to provide more enrichment such as might be needed for cold starting eliminating the conventional choke. I think the cold start function on this Suzuki carb is controlled by electrics.
Here’s a video showing a pair of SU carbs that might be off a circa 1960 British or Swedish 4 cylinder >>>
http://www.youtube.com/watch?v=YH6306zM-Ug
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