That's the typical axle sprocket for a Yerf Spiderbox- pat her on the back for counting correctly!!!
With the engine running well then the next place to look is the CVT as suggested earlier by x-bird. Wore out rollers,worn belt,clutch pads or spring could all be reasons for slower than normal speed and fairly inexpensive repairs. When you get the cover off the cvt (with rear wheels elevated) watch it running and verify the belt travels all the way up & down the pulleys to start with. Let us know what you find out.
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