That's a novel idea...With a spark plug that looks like that, before I’d go after the valves I’d be checking to see if the choke is fully open.
I have tried new plug, but not re recently.
Its never really run that well. But has recently deteriorated to stalling and even back firing.
Like I say just fitted new carb, but no real improvement.
I've done the obvious like filters etc
it's a single cylinder engineFind out if just one cylinder is causing problem by disconnecting one spark plug wire then reverse. May be sticky valve on bad cylinder if just one cylinder