Sorry for the late post... I hope its still useful.
Bogs with the Solex 4A1 can be caused by several things. Here's what I've seen with my own Solex'ed 250T (now gone).
There are two ways a working accelerator pump can cause the bog you described. Either the pump shot is late or the duration of the pump shot is too short.
My observations with the accerator pump on the Solex 4A1 is that the accelerator pump lever should *just* touch the accelerator pump's piston when the engine is at idle and the engine running. Otherwise, the shot would be late and you experience a bog then it goes.
Then there's a adjustable screw mounted on the accelerator pump lever itself that limits the travel of the piston -- my observation is that controls the duration (and quantity) of the pump shot.
A late pump shot would go: bog... vroom.
A short pump shot would go: quick vroom... bog... vroom
dirt in the idle jets and main jets can manifest as bogging down when accelerating from a stand-still.
Sticky secondaries (meaning the secondary plate doesn't open) doesn't show up as a bog... but rather a loss of power/grunt at 4000 rpm up.
Secondaries that open without giving more fuel will bog down the engine. A loose air-flap can do this, or blocked secondary fuel circuits, or an empty secondary fuel-bowl.
Oh yeah, before you start tearing up your Solex... have you checked your ignition timing? dwell? etc?
Hope that helps,
79 350SE (W116)
86 230E (W124)