i have a Miller Maxstar 200 SD. it welds perfectly with a 1/16 tungsten ( 2%)electrode but when i switch to a 1/8, it "spatters". i just bought a new collet and it didnt make any difference. machine is set at 180 amps. using foot pedal. gas set to 20. tried two different bottles-no difference with the 1/8. the weld comes out porous like its contaminated but when i switch back to the 1/16 it welds just fine. no porosity, no "spattering". any ideas what i could be doing wrong ? possibly the machine ? thanks in advance .