Repairs 22in toro recycler with 6.25 tecumseh

So i was given a toro 22in mower in reasonably good condition although the blade was so dull it was rounded over and the oil was like sludge. I finally got it to run after replacing a completely clogged air filter. I proceded to put a new plug, changed the oil and got a new blade. I also removed the carb, took off the bowl looked inside and it seemed fine so i put it back together. it then ran for about 1/10th of my lawn while back firing every once and a while and i let go of the handle to move a rock and when i went to start it again nothing, although now it makes a clunking sound when i pull the lanyard and sometimes when i pull it stops the lanyard before i get a full pull. And the SOB wont strt for love or money so i figured i must have done something wrong so i took the carb back off and took it apart again but everything was right so i put it back on and still nothing. I checked for spark bu holding the plug against the engine and having a buddy pull the lanyard but i can't tell if there is spark or not. i hope someone can halp with this isa a pretty nice mower. also when the banging started i chacked the blade because i figured i didn't tighten it or something but its secure and the right one so not that. thanks folks