I just fixed a FH500 that ran just like yours. On my buddy's mower the valve guide moved and the valve stuck open. I pulled the head and carried it to a machine shop and another friend of mine fixed it. Runs good now. So get a second look at it. You may not need to replace the engine, but hows the oil level?
All equipment is wore out.
<- Never mind. All equipment has been repainted and with new decals. It's like I have new mower's again!
48" Ferris WB
36" Ferris WB
All Echo hand helds
<- That's how I feel at the end of the day.