Ditto, I'd lower the wire speed a little too,MIG welding? Turn up your heat and slow down a bit.
but try Higher AMPS lower speed wire.
Clean metal = Clean Welds. Get that metal ground clean and you'll get better welds. The cleaner the metal, the better the ground which helps as well. I usually clean my metal with brake cleaner after it's ground to remove all grease / oil as well. You'll get even less imperfections. A master fabricator at a motorcycle company showed me these tricks years ago. Granted, there are other tricks as well, but good clean metal is critical. Also, use good 1018 CR steel. Junk HR steel, and plated steel does not weld well.