I have a Hustler Fastrak 44” Model 926519 with a Honda GXV610 18HP engine.
A couple of years ago it started running strange. It wouldn’t go up to full rpm, after running a while it would all of a sudden go to full rpm and power and run that way until I shut it off.
Now it will not come up to full rpm. I have replaced the fuel filter, air filter, and spark plugs.
It will not cut heavy grass unless I move very slow.
documoto.digabit.com
see Troubleshooting page 6.1 "loss of power" in manual above.