When trying to start it backfires & makes quiet popping noise. Sometimes acts as if compression relief not working.. I already have changed sparkplug, igniter, coil, Checked flywheel key, soaked carb. In carb.cleaner. Also checked valve clearance. Compression relief does work.

Hi,
Sounds as if you still have a bad igniter. Batches have turned up at times.
Peace,
Clarke