90 amps in a welding machine is hardly enough to do anything. Certainly not weld more that 3/16". The rule with welders, same as anything, is you get what you pay for. And you, sir, have not paid for very much. The erratic arc operation is obviously due to your wire feed speed being way to high, and your machine not being able to produce enough current to melt the end of the wire fast enough, and thus sustain a smooth arc gap. If you want to get a little more technical, frankly 90 amps isn't really enough current to be flux-core welding with wire of any size! Flux core inherently requires 50-100% more current than a solid wire of the same size in order to produce good welding characteristics. The reasons for this have to do with the way the metal is transferred through the arc compared to hard wire. (If you really want to know just email me.) But suffice it to say flux core requires a lot more current than gas-shielded solid-wire MIG. For this reason I would not recommend using flux core wire on anything below 1/8, which as I mentioned is too big and requires way to much current for your tiny machine to handle. The first thing I recommend is investing in a good 220 volt welder, if you're actually serious about welding. The second thing I'd recommend is to get a gas regulator and start using gas-shielded MIG. Solid wire costs about 1/3 as much as flux-core. Gas isn't that expensive. A spool of hard wire plus a bottle of gas combined will generally cost less than a single spool of flux-core. You'll save money in the long run. The third thing I'd recommend is stay away from the self-sheilded flux core entirely, that stuff is total crap. IMO it's the worst welding process ever created. (hope you enjoy breathing the toxic fumes from that stuff BTW) Good luck.