I have just replaced the pads on the above mentioned mower and still do not have brakes. I have adjusted the middle nut on the caliper, which used to give some brakes, but now it doesn't help. Is there another adjustment I can make to be able to cut grass safely? Please help!

I have a Craftsman 6.75 rear drive self propel mower that a friend of mine gave me a few months back. I used it most of the summer. The self propel was acting weird so I replaced the belt, I found out after taking the blade off that the lower bearing support on the blade end of the drive was missing all of the ball bearings (looked like it had been for some time no idea why), but that part is no longer available so I just put it back together with the new belt. It worked alright, threw the belt on the rear drive end a couple times but no other issues. About a month ago I got it out to mow and noticed when I started it up it was making some kind of clanging noise, and it threw the belt. I fixed the belt, started it again and it again threw the belt and was still making the noise so I turned it up on its side to see what was going on. When I went to take the blade off I noticed the blade bolt wasn't tight, and then after removing the blade I found out the blade adapter was cracked almost all the way down one side. I have no idea how this happened as I don't recall hitting anything and everything with it was fine when I put it back in the shed the last time I used it (I keep it locked up). I took everything apart and ordered a new blade adapter off the Sears Parts website. I noticed when it came in it wasn't exactly the same as the old one but it seemed to fit OK and the blade cleared the deck and everything else fine so I figured it wasn't an issue. Well, now it won't start and I'm not even sure what it's doing. When you pull it, it sounds like it tries to start and a couple puffs of black smoke come out of the muffler, then it kind of kicks back and smoke comes out of the carburetor (I know that's not good). It's also making a weird sort of knocking sound when you pull it and it turns over (not really sure how to describe it, sounds like something is hitting something else). What is it doing and why is smoke coming out of the carb?