Welcome to the site shixanget...
Start by pulling the carb off, and give it a GOOD cleaning, pull all the jets out and blow compressed air through all of them, and write down all the current jet sizes for reference.
While you have the carb off, pull the reeds out too and check for broken petals, and/or gaps around the edges...the reeds should be sitting flat all around the reed block. If there are gaps, you can try to flip the petals over...but if that doesn't get them to sit flat, you may need to get a new set of petals.
Toss in a new spark plug if you have one...gapped at .024, and verify it for spark....put it all back together, throw some fresh fuel in it...and see if it'll fire up and run like it should.
It would be a good idea to get that crack in the pipe welded soon, or it could get bigger....or buy a new or used pipe....but if it's just a hair line crack, that shouldn't cause it not to start.
Let us know how you make out....if it's not better, a compression test, and a leak down test may be in order...but it sounds fuel related.