Can`t hurt to clean them , not sure what will work best though
BP gas is supposed to clean it.... or just start the motor and pull a plug and fuel wash it
I had a plug wire come off one time and when I pulled the 906's that I sold shortly after the whole combustion chamber and those 2 valvs were completely cleaned of deposits... "Fuel Washed"
I dont think I would recomend doing this. but it works ,,,,,,,