[Roadsters] Choking [was: How to warm up a Roadster?]

[Todd Osborn]

John F Sandhoff wrote:
...On a 'standard' carb such as a Solex, there's a physical air restrictor
plate that reduces the air admitted. Same fuel, less air = richer
mixture. "Closing" the choke richens the mixture by suffocating
air flow...

Since when are Solex carbs considered standard (ahem!). Turns out the
Mikuni/Solex carbs don't use a butterfly valve to "choke" the air flow. They
use a fuel enrichment circuit similar to the Weber (or maybe it's the other
way around). Applying the choke rotates the starter disk that applies vacuum
to the starter circuit, pulling fuel from the float bowl through the starter
jet, then emulsifying it with air and then releasing it through a port on
the engine side of the throttle valves. Note the very early Solex PHH carbs
(old Alfas and Mercedes 180SLs) did have a conventional choke valve, but
these are really a staged two barrel carbs with a primary and secondary
throat and have almost nothing in common with the Mikuni/Solex 44PHH design.
In my climate I have found that the accel pumps on the Solex are large
enough that one never needs to use the "choke".
Todd Osborn
DATSFUN
San Jose, CA