Black spark plugs

Would assure choke plungers are in their full down position when choke is off.

There's a soft (rubber?) gasket at bottom of choke plunger that closes off the starter fuel passage when the choke is off (plunger pushes down against the starter fuel passage exit). It's possible for such gasket to fail whereby the choke (enrichener) circuit continues to partially function although the plunger is pushed all the way down. Thereby contributing to over-enrichment of the fuel mixture.

Good Luck!