Small Engines (Lawn Mowers, etc.): Honda HRX217HXA idling problems, speed circuit, carburetor

Question
I have had the mower two years now and at the end of last season the mower started to display an inability to idle properly with the blade disengaged. When the mower is left idling in the "fast" mode the idle RPM will increase and decrease which will eventually become worse the longer you let  it go. If you try to move the idle to "slow" the mower will idle for a short time and then will stall out. The weird thing is that when the blade is engaged there are no problems with the RPM what-so-ever. Before putting it up for the season last year I ran the tank with some stabil in it before storing it in the garage. I have checked the linkage and everything is hooked up properly. When the idling with out the blade engaged you can see the lever that controls the carburetor moving up and down. If you physically hold this the idle will then stay constant. I have tried running the mower with the air filter off to see if it made any difference and there was none. I'm at a loss and my two year warranty was up today. Thank you for any insight that you might have.  

Answer
Your symptoms are typical of a dirty carburetor.  When the blade is engaged the high speed circuit of the carburetor supplies fuel to the engine.  Since the engine runs decent with the blade engaged then the low speed circuit of the carb is the most likely cause of the problem.
Have you removed the carburetor bowl to see if there is any debris in the bowl?
The repair is to remove, dis-assemlbe and clean the carb with compressed air from an air compressor.  You can also spray carb cleaner through the carb orfices to enusre there is no blockage in the fuel circuits.
Let me know if this helps.
Eric