After a lot of hard work with amateur skills, I got my YT11 working again!
I rebuilt my carburetor (kind of twice) but the flywheel key kept shearing. I went online to try and figure it out as I was afraid that something internal was bent. Instead I finally read that you really have to crank down on the nut. That did the trick and it started running pretty well. I went online to see what the gap of the magneto was supposed to be and somebody said .010. So I set it at that. It was running rough so I finally found the engine manual and it said the gap was .020! Twice as wide. So I readjusted it and that made a huge difference.
A couple of tire were leaking, but I put in some of the green goop and drove it around at high speed and they seem to be all sealed up.
I still need an original gas tank. But I am driving it happy.