Toro not starting

I know this problem has probably been asked time and time again, but every problem (with engines) is slightly different, so here's mine:

My mower was running last year (notice I did not say running fine, it was just running) it would run for a bit, then stop, or you'd have to stop after a couple passes to let the engine cool, or remove clippings from the housing. Either way, it worked.

This is my fathers mower, and not mine, so I was not able to help him with it last year, that aside, I came back this year and tried to start the mower, to no avail.

I'm not a big small engines guy, but I'm willing to learn, and I have more than enough tools at my disposal, granted they are more suited to working on large turbines, haha.

So my story begins as such, My father tried to start the mower this spring, and it would start, then sputter, then shut off. He figured it was a problem with the gas line, so poured a bottle of gas line anti freeze in the tank, then he topped up the oil, when I asked when type of oil, he said, one of the bottles over there. There were two car oil bottles, and one two stroke engine oil, so he might have put the wrong type in.

Anyway, I started tinkering, doing small maintenance things, drained the fuel, removed the air filter, which was dirtier than a babies diaper, so I figured had my father changed that right away, it would have been fine. Either way, I continued along the fuel path and removed the carburetor, it wasn't bad. So I replaced the air filter, used to carb cleaner on the carb, and replaced the spark plug. Refilled the gas tank with premium fuel. Gave it a yank, and it's still not going. The plug I pulled out was an RJ19LM, which I can only assume is the exact same as a J19LM.

Now I've been looking up online some solutions, and I haven't really found any to my liking, I've read that it could be the flywheel key, which would make the spark out of synch, but I never actually hit anything, so I don't know why it would be that. I haven't changed the oil yet, because I didn't think it would make much of a difference, but if you tell me to, I'll do it right away. I didn't inspect the muffler or anything, I can't see that causing a problem, so basically I'm wondering if I need to start learning about small engines? Or if anyone has any other suggestions I'd love to know, thanks!

(Sorry for the long post, but thanks for reading)

Usually a mower that has sat for a while with gas in it will have varnish buildup somewhere in the fuel system. A visual look at the carb my sometimes look ok, but it is the small orfices that cause the problems. It is best to poke them out with soft tag wire, then spray them with the carb cleaner. Some of those passages are so small that a tiny speck of debris will cause a clog.

Sorry I forgot to say, I did use a wire from a garbage bag twist tie after I stripped that plastic off to poke all the holes

Dump a tea spoon of gas in the carb and see if it runs for a sec and dies if this happens you know you have a good engine. Now it is time for some carb work/adjustment or a carb rebuild may be in order.

ok, when you say in the carb, I assume you mean the bowl? I'll have to do that step tomorrow, as it's dark out now, but what if there is already fuel in the bowl? can I disregard this test? or should I empty and test with new fuel? Also should I prime it as well? or is that basically what putting the teaspoon in the bowl does?

Ok I got it figured out, I guess there was some gas in the motor that was still bad or something, what I basically did was hold the throttle plate open on the carb while I sprayed some carb cleaner, it sputtered a few time, and I help the plate open while doing quick sprays for about a minute, then shut the throttle plate and it reved up nice, then let it run for about a minute or two, shut it off, and it started back up fine.

Thanks for the suggestions