Every. And I mean EVERY Barry Grant carb I have touched (OK, it's only 4 of them, but it was all of them) had debris inside. Shavings and such. A dirty carb really makes tuning hard.
I second this remark about questionable factory-delivered condition of Barry Grant carbs. The thing I heard, though, had to do with ensuring that the float level on the carb is dead-on. Maybe give the thing a once over just to be sure it is set up well.