Older SCAG STC48a-21KW (homeowner)

Symptoms: Was dropping power on relatively high grass. (5"-6" tall). Then it was struggling to go up hill (small hill - with blades engaged). Then this past Sunday it died. It will start up with the choke pulled. When I close the choke - it dies. I needed to run it on "partial" choke just to park it in shed. When I run it on "partial" choke - it revs up nicely .....then it slowly comes back down and dies.

My troubleshooting plan:
a) check/replace plugs;
b)...

Older SCAG STC48a-21KW (homeowner)