I'm not sure what engine kit it was. I buy engines from various sellers for installs on bikes that I build to sell.
One every engine I buy, regardless of seller here is what I do:
1. replace all studs except head studs
2. Remove cylinder and head and loctite the cylinder head studs.
3. Home made thicker intake gasket coated with gasket maker
4. Loctite the carb main jet (had one fall off during a ride from vibration)
5. Loctite the main drive gear (the one that got loose on you)
6. Loctite all mountain bolts after engine is properly aligned with chain/sprocket.
7. Replace spark plug with USA made plug or non-China plug (center electrode can pop out on you during a ride...don't want to get stuck in middle of no where and be forced to pedal)
8. Replace spark plug wire with quality Bosch or equivalent plug wire.
9. Use 6mm couplers as nuts for all engine mount bolts. This gives the coupler nut more thread to grip and allows me to torque to stretch the bolt just prior to its point of elasticity. With loctite, I never have a loose engine mount.