Only one speed on this model (gear box type unit). Should propel at 4.0 km/h (2.5 mph) if set-up correctly. Mae sure the throttle is always set to FAST. This will get you the fastest travel speed, as well as the highest quality cut. Blades must spin very fast to get a quality finish.
Did you buy this new? If you don't think it is working properly, get it to your local Honda dealer, and they can verify the engine speed is set correctly, and do a full inspection and evaluation. Factory defects are generally covered under warranty, but be sure to confirm what will or will not be covered before authorizing any work.
Here's a link to find a servicing dealer in your area:
Find A Honda Dealer