I believe Karma solely comes from upvotes for comments minus downvotes. Submissions don't count.
Although nothing is crystal clear, the karma system is not 1:1 for submissions.
<https://news.ycombinator.com/item?id=29024032>
Comment upvote +1
Comment downvote -1
Submission upvote >0 && <1 (not documented to prevent abuses)
Submission downvote not possible (only flagging is allowed)