Welding advice

[CaptainCrash1971]

Hi Folks, some feedback please
I bought a Clarke welder 2nd hand off ebay a few months ago, but have only just gotten round to having a play.
I've got it set up with 0.8mm wire, new wire guide, disposable CO2 bottle (until something better comes along), and used some 1.5mm thick 25mm square box section to practice on.
After a couple hours messing around, I got the following welds

1.jpg
I cut the box section open to show the reverse off the welds.

2.jpg

I then used the settings from the 2 welds on the left to weld two pieces of box section together. The result was rather messy, but seems very solid (have done hammer test). The only problem is, when I cut it open, there doesn't seem to be any penetration on the other side, just some discolouration. Is this OK, or should there be some weld penetrating?
Anyway, three of the welds are shown below
3.jpg
4.jpg
5.jpg
Any help/feedback would be appreciated. Will hopefully be able to get back in garage tomorrow and practice with whatever advice I get.