I have a 2hp briggs stratton on one of the few mii bikes/gocarts I have.

It was running fine idling,I gave it a bit of gas,let it idle,, and gave it quite bit more gas and it bogged out and died.I was also messin with the jet finding the ahppy spot.

Took the ehad off,valves aren't stuck,rings are good,brand new inside of the cylinder,pistons clean and ice,
I'm getting spark
Good compression.
It was ran on 2 stroke gas for 5 minutes(my brother).

'and it backfires through the carbuerator sometimes.whats wrong?
Yes the coil and mag pick up magnet are clean
All good gaskets and seals

Clean the fuel system including carb, and replace the fuel filter if there is one.
Check flywheel key.
Replace plug.
Re-adjust carb. If two screws the larger is for high speeds and the smaller one is for low idle speeds. Use 1.5-2 turns out from fully in as a start.

Flywheel key could be sheared.