Troybilt

We have a Troy bilt model 42049 snow blower.  Starts fine , 1 - 2 pulls ,  it is well maintained.  my question - I've noticed @ full throttle blowing snow  # 2 speed ,  machine rpm's are good but  into a bit deeper snow it never seems to engage the governor ??  fast speed is 3400 rpm with a digital tach.  the machine is old but it is spotless not rust at all. oil changed every fall and a new plug.  ???    Thanks