Re: My chain is saggy
I really don't think a springed tensioner is a "need to have it" thing, it's kind of a luxury thing.
With as much slack as you've got, I would seriously pull links out. Optimally, you don't want to have the tensioner right up on the sprocket, which I assume is the only way you would be able to adjust it, even by maxing the pulley to the very top.
On the spark plug:
There's a crush washer that should keep it snug, I would really put money on it just not being put in tight enough, or the crush washer going out. You can replace the crush washer, though, I would also have to assume it's a chinese plug that came with the kit, and they're honestly junk.
Worst case scenario is that the threads in the head are going out - which of course we are hoping is not the case. So you know, locktite won't do it, as it's removed with heat, and once it's fired up the heat will be enough to where it wouldn't cut it.