Points that are adjusted properly will show very little spark, but technically, they spark every firing.
We need to see if you are firing a spark on all 4. Get a clean spark plug, a d8ea is preferred, and check to see that every single one sparks.
Again, you are fouling on at least 3, which means you have spark on those at least part of the time.
Please do these things in order, otherwise we get out of order and can't tell wtf is going on.
Check for spark on all 4.
Lets find out which way is choke-on on your carbs, I believe it's 'back', but I can't remember offhand.
That measn once it's warmed up (and the 350's warm up pretty fast, they are so small), you need to run it with the CHOKE OFF, otherwise you'll foul the plugs... just like they are fouled now, and they won't run anymore.
You need a full set of plugs again anyway. Like I said, these bikes never run right on 'cleaned' plugs after they've been fouled.