Doesn't want to idle unless choke is on, back fires when l Etting off throttle.

 

First thing is clean the carb out. Remove float bowl, remove jets, blow them out with compressed air. blow the holes they came from out, check the jets are clean by holding them to the light, clean the float bowl out, re-assemble.

 

Try to determine if the backfire is thru exhaust or intake.
If it's the exhaust you may have an exhaust leak. Mine had a leak at the gasket between the pipe and head causing a backfire.
If it's the intake most likely it's lean. Intake leak or carb malfunction.
I would guess intake side as it won't idle.