They generally breathe well enough to avoid clogging... that's not to say it doesn't happen.... too much carbon released all at once thanks to the brilliant use of seafoam or similiar... too much soot from run deadly rich... collapsing of the catalyst structure due to significant vibration or a couple bad hits to the front of the unit.
How quickly is the turbo spooling? What kind of mileage are you getting? Have you checked for exhaust leaks?
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