TIG welding problems...help!

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Hello, this is my first post on any web site dealing with welding. I hope to find some help here.I have a thermal dynamic tig welder that i have been using for about 5 or so months. I am somewhat self taugh at welding (along with mechanics, machining, ect...) very much a novice at all of it. Anyways, i am building an old harley chopper and my welds have been good. All seems to be well, then all of asudden about 3 months into having my unit i get spatter and holes in my welds, along with usually yellow and sometimes white smoke around the weld area and on my cup. This goes off an on as i weld, but it especially seems to happen on thicker metals. When i say off and on i mean it will be fine for a few inches, but then something happens to set it off, then it may, or may not, get good again in other areas of the weld. I weld mainly mild carbon steel (round stock and sheet metal). When my welder is working i can get great welds, but when this happens it throws acceptable out the window. My argon flow is between 15 cfm and 20, i have even experimented with 25. Im using 2% th tungsten sharpened like a pencil parallel with the length of course, size 12 lens, i clean the daylights out of the welds ( sandpaper, acetone, lint free clothe, let dry, and so on- another words i get it clean.) I cannot for the life of me understand what is going on. This may add a clue for some of you. Before i had this machine i had a new syncrowave 350lx, and it worked for a while then started doing the same thing. the guy i sold it to however has had no problems at all with it (bad electric input)? I am going to post some pics, along with my project, to show you what i am speaking of here. i fabed the gas tank, and other not so noticeable parts. and check out the pics of my welds when the machine is working (i wont point which are the bad and good because its more than obviouse) Attached Images
Reply:more pics...i could only upload five at a time. check out the kick only 80'' shovel. rigid frame of course magneto, SU carb. yea baby! Attached Images
Reply:For the welds, you have a coating on one of your pieces.  It could be zink or galv.  It could even come from the inside of the pipe.  Grind down to bare metal inside and out.  My guess is that will do it.I think I can see the coating at the arc mark in picture #3.I like the bike and the kickstand.  David Real world weldin.  When I grow up I want to be a tig weldor.
Reply:Picture 1,2,3 all lacking gas coverage. Causes include cylinder empty, lose fitting between the cylinder and the work, cylinder not opened fully, holes in the gas line(sucking atmosphere into the gas flow)Cool design on the fuel tank.TJ
Reply:dont you find the seat design a bit brutal?consider changing the plug for a cushion.....
Reply:My first thought was gas coverage but a possible coating on the metal makes sense too.I saw the same white or yellow/orange substance when I built a mini chopper. I used nuts and bolts to make up the motor and tranny and resulted in the same look. So my guess would be a coating on the metal. Just my two cents...
Reply:Is the torch water cooled, If so your stool wouldn't be sitting on the gas hose, closing off the gas hose, would it? Sounds far fetched but I have done it more then once.Tim Beeker.
Reply:Looks like gas problem... Either supply is not good or mixture with pipe coating fumes produces wrong shielding...