I would look at the choke plate in the carb to see if it is opening fully. With the engine shut off, I would remove the airfilter so you can see what the choke and throttle plates are doing when you move the controls for each. You may have a throttle/choke combination where you move the throttle lever to max to get the choke to close and when running you move the lever away from the choke position. In either case, you may have a broken cable or just out of adjustment. Vibration has a negative effect on machines and periodic readjusting and tightening of some things is necessary.
I gotta go and do a 50HR service on my Scag ZTR.
Mad Mackie in CT:biggrin::laughing: