I had the same sorta thing happen with my os 32 and 50.The mixture seems to be off and could set it no matter what.The plug in the 32 lasted about 2 gallons, it was a A3 I think.I replaced it with a A8 and it has lasted a lot longer.My 50 lasted about 5 gallons on a A8.So now I change plugs after 4 gallons max.The plugs never quit completely, just lost power and couldn't seem to be able to set mix.