I have a little four stroke mini baja bike. it is a 196cc home lite lawnmower type engine. a few weeks ago i changed the oil and i think i over filled it. now the plug fouls constantly within the first few minutes of use. i tried getting a new spark plug but it did nothing. what can i do to fix this problem? please help.... this was my birthday present last year and it sucks because it starts, but it loses all its power almost immediately and i end up pushing it home.