Tractor Repair: case995xl engine, white smoke, washers

Question
engine rebuilt,pump&injectors done engine firingon pistons 3&4,not firing on 1&2 only white smoke,engine timing seems ok

Answer
is it possible that some of the copper washers on the injectors didnt come out when you removed the enjectors and when you got the injectors back you put 4 new copper washers in so two of the injectors might have ended up with two copper washers instead of one ive seen it happen