I have a Troy Bilt 17.5 HP that's hard to start and it turns over very slowly or
Stops, like it has too much compression. I replace battery with a new one with
More cranking amps and still hard to turn over. Check the starter and it seems
Okay. Removed the spark plug and it turns over freely, so it must have too much
Compression but I don't know what to do now.

Thanks John

Hi,
The likelihood is that it needs a valve adjustment. Look at:
YouTube - Lawn Mower Repair Valve Adjustment
To see a video describing the procedure.
Peace,
Clarke