hi Gary the carby you are talking about is G4 carby, it is pos to bring the idle down, but hard to explain, if you have ever pulled one of these carbys apart there are alot of moving parts diaphram,vavle,two springs, cam,cam lock, ect.I will give you as much detail as pos,firstly i need to tell you not to touch primer/float bowl its nothing to do with idle. O.K take carby off mech by twisting down ,then take off diaphram cover with screw driver, note large spring ,then diaphram remove diaphram by moving washer to one side then pull off diaphram note smaller spring then cam lock (three leged has this side up on it)remove noteing how it goes back, next remove air filter snorkel , move the throtle controll on handle to the stop position but first take out kill switch wires one has a rubber cover on it then remove throtle cable , it needs to be in the stop position to remove, once the cable is out remove cam, now what is goeing to slow down the idle is a very cheep small washer that you need to buy from a mower shop , it goes on before you fit the cam, that brings the popet valve closer to its seat at idle,install the same way as removed best of luck jason
jason
December 2007