cette pièce qui tombe est probablement le jet d'aiguille, il est fait pour s'adapter correctement d'une seule façon. certains des jets d'aiguille s'adaptent parfaitement et d'autres assez lâchement j'espère que cela répond à votre question je vous ai répondu en utilisant google translate
Here is a suggestion. drain the oil to check for anything odd in the oil if nothing take the spark plug out have a look in the spark plug hole next put the bike in 5th (top) gear try to pull the bike backward you only want to turn the engine a very small amount once the engine has turned over backward a small amount try to look into the spark plug hole next take off the water pump cover and make sure the impeller in intact next I would have a look in the clutch side cover I would not suggest trying to start the bike until you find the problem
what has happened seems odd GOOD LUCK