By winding it over a lot with no spark you have just wet the plugs...
Stick another set in...
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Wetting or fouling plugs after cranking is usually considered to be a two stroke only problem (two strokes can be fair bar stewards in this regard)....however...and for what it is worth...
Over the years, I have managed to start many stubborn engines just by pulling the plugs and carefully cleaning and drying them....by doing this, you are always giving the donk the best chance of firing.
So...pull the wet plugs and dry them excternally with an absorbent cloth. I then get down into the inner part with a very small screw driver covered in cloth. I also use a small screwdriver to scrap stubborn carbon deposits away. Make sure you get an absorbent rag all the way down around the bottom of the insulator post...I do this with the very small screw driver covered in cloth.
I also use wire brushes made from "File Cards", these are the flat boards with a wire brush glued to them for cleaning files. I put these on a band saw and cut them up into 3 or 4 long skinny plug cleaners (I make em a bit over 1 cm wide). I use these to brush away all the carbon scale from the plugs (because I'm too lousy to buy a plug cleaner!)
(and be patient, sometimes you might have to do this multiple times whilst trying to find that dud plug lead, cracked dissy cap or dicky points)