Hello,
if I may allow myself a suggestion. After watching your video, it seems to me to come from carburetion.
With the engine cold, do a test by pouring a few cc of petrol directly into the carburetor or by spraying brake cleaner (beware of the flashback that could occur if the ignition is out of order)
Please excuse my English, because I am in a region where French is spoken.
Have a good day
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