What size wire are you using? If you are using the .035 size, maybe you will have better luck with the thinner wire. If you can stabilize your power source (wire it straight to the breaker box, big fat extension, don't run other tools or appliances, etc), that can help too.
But honestly, I was never able to overcome the problems you describe with my old flux core welder. I finally ditched it got a small name brand MIG welder with the gas shielding and that kind of welding turned out to be so much better.