I did valves adjustment and I do not notice any improvement;-Have the valves been adjusted recently? if not mite be your issue.
It explodes for the carburetor, I'm uploading a video so you can see itI'm guessing you mean it back fires threw the intake / carb?
-If so, clean carb and verify it's settings and check the intake boot to the engine for cracks etc...
-fresh fuel if not already done.
-New spark plug
it's for crack of intake boot to carburator, no problemYour last vid was too dark to see(for me) where that spark flash was coming from BUT the high tension lead from the spark plug will do that, replace it if that's where it's coming from, can you get a pic of that area with more light in it?? Do not ride it until you cure the spark problem, that spark could ignite any fuel leak