It is all practice, and settings. Flux core can be a pain to get dialled in. It's also more picky about cleanliness, all surfaces need to be super clean and shiny - no rust, scale, paint or oil/grease. I always take time to quickly degrease any surface I'm about to weld.
I tend to find on long runs doing the "e" shape helps with flux core, rather than just one long line.
Spatter is the downside to flux core. I get the same. You can get anti spatter sprays but I'm not keen on them as they are mainly silicon based, and I paint after. I tend to use a fire blanket to cover areas near the weld to stop it going everywhere.
I am running same welder on my build. Dont expect perfection off flux core. I had same issue with high and low spots and spent a ton of time trying make look perfect. I finally decided that it’s a home build and im not a welder and as long as structurally sound IDC about appearance
Flux core is a lot like stick welding with a welding rod, except the flux is inside of the wire with flux core (fcaw), opposed to the flux being on the outside of a stick rod (smaw).
To avoid some of the spatter sticking so much, you can spray anti-spatter spray on your base metal before you weld. I like the dry spray, it goes on wet then turns into a dry white powder which can be wiped off without any residue. This'll make it a little easier to scrape off the dingleberries, which are inevitable in this welding process.
Also Boom mentioned practice. if you can slow down and let the weld fill in at the low spots in order for the weld pool to fill in. And learn how to read the weld pool. If you have gaps on 10 gauge, you may need to turn the setting down to 14 gauge so that you are not blowing holes.
On that note, fit up is important. If some parts have gaps and some are tight fit, then it wont weld the same,. An experienced welder can compensate for some of this, but often a bad weld is due to poor fit up. Practice these things and you should see some improvement..
I sound like a broken record but flux welding is definitely not the most efficient method and as long as your pieces are melted together, call it good.
With that said, try turning your temp down a half notch to see if that helps. You may need to then turn your wire speed up just a bit to allow more full metal. Remember that a portion of your wire is flux so does nothing to add to the weld fill. Being outside in ANY wind is also going to blow your heat all over and decrease weld effectiveness.
Welded some 1/8 wall tube to some 1/4” thick angle for my dad yesterday for a dueling tree build. Cranked the heat and feed up a bit, slowed down and did the “e” shaped or triangular shaped drag and it seemed to fill up rather solid.
Will try this again on the tubing and see if I can get similar results without warping anything.
Can anything be done to the pits/low spots in the welds I already have to make it look a bit better for paint?
Body filler can be used nicely on many projects to smooth out edges but not sure I'd try it for a project subjected to heat cycles like a smoker. Your best bet it to "spot weld" the holes and start the grinding process all over. Problem is, this can run you down the rabbit hole pretty quickly as you need to keep repeating to make it perfect and end up wasting a bunch of time. This is especially true with flux as you will have a bunch of splatter to clean up as well.
I find myself dressing fewer and fewer welds lately and embracing the look of the bead. Grinding everything flush tends to eat up a lot of time and weaken the joint so it's a win-win to leave it alone in many cases.
The area in question, is on the front end of frame where it will attach to axle for steering. I can’t imagine it’ll be subject to much different heat properties than the hood or front fenders of a car, so I may try the bondo idea, there.
As for the rest of the frame, I may just brush the top of welds with flap disc as I’m cleaning up splatter, instead of grinding flat. We’ll see