I just had this same problem on a 9.8 hp Nissan 2 stroke... I run nasty bad fuel through it by mistake... the fuel was 9 months old and was rusty brown... the fuel gauge was metallic and it was covered in orange gunk.  Got new gas and a different fuel tank.... flushed fuel line... back flushed Nissan fuel filter...I took the carb off and sprayed carb cleaner through it … put it back on and engine would barely run.... took carb off again and sprayed more carb cleaner... second time really sprayed every hole in the carb both ways if possible.. used an entire can of cleaner for this tiny carb... put it back together, and it ran great.. like brand new... Jim Gano