The plastic carbs used on the modern OHV Briggs engines are known to be very sensitive, mainly because they jet them very lean that it doesn't take much to cause the sort of running condition you have described. This applies to the 125, 140, 150 and 163cc engines, I think they use the same carb on the larger-block 190cc engines too. In any case, you will need to remove, disassemble and clean the carb.
These video are quite long, but very informative regarding these carbs -
