My understanding is that the flap in the offside exhaust is totally unrelated to the type of choke you have. The choke on the carburettor provides richer fuel to get the engine started. The flap in the exhaust shuts down the offside pipe which means exhaust gasses from that side of the engine have to pass through the inlet manifold and exit via the nearside exhaust, warming the inlet system as they go. As the engine heats up the bimetallic strip opens the offside exhaust and both pipes come into play.
The flap valve should regularly be lubricated with graphite. The easiest way to do this is to use an aerosol of penetrating oil with graphite. A little tricky to find but I have found it on Ebay.
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