This is not uncommon to a set of SU's running a little rich. Once the carbs, and not jus the engine warms up the fuel level rises a bit and runs a tad too rich. you reall need to do the tune when the engine is and carbs are warm but not hot.
First question, which needles are you using?
Is the engine/airflow modified?
does the carbs have lift pins?

My first assumption is that the carb jets are set a little too low (rich). 11 flats is too low even for a modified engine, depending on which needles you're using.

The way to do this is to lift the pistons, one at a time. and have the idle rise just about 50 rpm while idling at ~650-700 rpm. The rpm rise should last for 2-3 sec then settle back to the set idle. If the rise is greater or longer, the carb is running too rich. If the rise is not noticable, or drops, the carb is too lean. Back off the 11 flat position until you have no change when lifting the piston of the oppposite carb. Do this in small changes for each carb until both have the same small rpm rise and fall.
This is somewhere around 8-9 flats, not 11 flats. When youre done, raise the idle to 900 rpm and turn each jet nut 1/2 flat lower (back off).
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'89 245 Sportwagon, '04 V70 2.5T Sportwagon