Small Engines (Lawn Mowers, etc.): Honda mower drive is slowing down, honda hrz216tda, honda manuals

Question
Hello Eric-
Honda HRZ216TDA self propel is not as fast as before. How can I adjust the cable to increase the speed slightly?

Answer
http://www.lawnmowersworld.com/honda/manuals/31VG4642.pdf

Looking at the Owner's Manual the TDA has a three speed transmission.  Cable adjustment will not impact the speed very much at all.  Do you have all three speeds?  I have had cables where 1st or 3rd speed did not work and if adjusting the cable did not work then the cable had to be replaced.

Is the belt in good condition and is the belt tension correct?  The belt may be slipping in high speed which may cause the speed to decrease.

Let me if the belt and belt tension are correct.

Thanks.
Eric