Small Engines (Lawn Mowers, etc.): B&S 12 hp on a Murry Select 2004, tiny circuits, ultrasonic cleaning

Question
QUESTION: I've cleaned the carb, intake, float bowl,jets,and everything else. The motor will only start and run on high with the choke on.
I'm stumped, any suggestions? Filter is clean and new too, and plug, and fuel.

ANSWER: What's the model, type and code number of the engine?

---------- FOLLOW-UP ----------

QUESTION: model-28R707
type-1120-E1
code-030826ZD
Thank you...for your time

Answer
The success rate for rebuilding these carburetors is very low.  They have problems with corrosion in the tiny circuits inside the carb body and just won't come clean.  I will very seldom bother with rebuilding them and almost always recommend replacement.  We use ultrasonic cleaning and still replace probably 90% of these carburetors.  Unfortunately, this may be what you have to do.