04 400ex SMOKING BAD fresh new top end

Put new top end on except for valve cover new piston jug was bored 16 over and the piston fit perfect but had issues with the oil ring on it guy said it was to long so he cut it a little bit and it fit put it all bacm together and I had issues getting it started turned out to be a timing issue and the vales were to tight got all that fixed started it and it is smoking something awful please help its a constant smoke !