Not sure if you have a Harbor Freight Predator 212cc Hemi Engine or not? The picture above is a quick way to know whether it's a "Hemi" or not.
Harbor Freight Predator Engine Numbers & Harbor Freight 20% Off Coupon
#60363 Predator 212cc Engine Hemi
#69730 Predator 212cc Engine Non-Hemi
sells a lot of aftermarket performance and racing parts for these engines.
The most popular "bolt on mods" are the Air Filter Kit, Jet Kit, and Exhaust.
Example: Predator 212cc Go Kart Kit - Stage 1 - Non-Hemi