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You can’r read the spark plug like on a 2 stroke and expect it to be brown or darker. these motors are just like a car motor.
The idle issue you may be having is most likely a vaccumm leak at the intake manifold or gasket, the engine cannot breath anywhere else other than the air filter area (front of carburetor)
Run that engine, let it idle on the stand, spray small amount of car/brake cleaner around the suspected air leak area, and see if anything changes after you spray.