I got some problems, the engine can't almost start, something it can start for a while ( 20 - 30 second) but in general, it wont start, but the engine make some explosion.

The spark plug become black ( I don't know the word , i'm not english )

The gaz get out from the air filter with high pressure when I try to start it ( every 4-5 seconds).

What it can be ?

I have a performance cdi and a big mikuni carburetor.

 

Is the spark plug wet (where it is black) when you try starting it? If yes, then you may be flooded.

 

I hav black on my spark plug also. I have it on the screw part that goes in to the engine and it is also on the part that the wire plugs in to.