Sidestand switch?
If you have the sidestand down in gear, it will kill the motor. In fact, you can use it for a kill switch. Back when my neutral switch was bad (and I probably still will), I'd simply kick down the stand in gear to park. I don't even need to touch the kill button.
Maybe if there's something going on with that switch, it would explain it.
I take it that it's not stalling from load.
Idle speed should be adjusted when warm. It tends to be kinda variable. There's a little fingerscrew on the carb to adjust idle speed. You can even adjust it at a red light. Giving it a little enrichment (choke out one or two clicks) may increase your cold idle speed. That's normal. Just keep it running at a reasonable idle speed (high enough to keep up oil pressure, low enough for control and minimal overheating or clutch drag) and you'll be fine. You don't necessarily need a tach. You can listen and feel for it to some extent, especially if you know how fast it's supposed to run. Go for a happy but relaxed sound. Not hyper, not dying... relaxed, secure, and happy.
Here's what 1000 rpm sounds like.
https://www.youtube.com/watch?v=rq_W5xhtjBwAnd 1100 rpm
https://www.youtube.com/watch?v=7WLURU50G-oI'm currently suffering from savagecharliefoxtrot or something, so we'll see what the others have to say.