Small Engines (Lawn Mowers, etc.): Lack of rpm with deck engaged, riding mower, fuel flow

Question
I just bought a used JD stx38 riding mower with a kohler 12.5hp engine and found out that I can't get the rpms up while the deck is on. While cutting, the engine seems like it's almost at low throttle yet the lever is at the highest level. Also the rpm's do increase slightly with no load and the engine quits at idle. I think I may have a dirty carb(cleaning or rebuilding). Starts ok, no surges, also I notice that to start it under cold or hot engine I have to choke it to start. Not sure if I have a governing problem or a carb.  

Answer
Hi Jim,

I suspect, as you do, a dirty carb.  That would limit the fuel flow and power.  Clean and rebuild the carb.  No power under a load, can also be a sign of a worn engine, which a compression test would indicate.

Let me know how you make out.
Michael