I just finished a full rebuild on my 350 (second time!!) due to letting someone else ride it and they broke the kickstart. I was originally going to open the bottom end only but I found the tensioner wheel was also seized and kind of exploded as a result. Anyways, a couple months later and it's all back together. It started up second kick and was idling immediately, although very low. I let it warm up a bit, rode it, and then raised the idle a bit manually once it was completely warm.
Next day went for a ride and it starts up again easily, idles fine, rides fine. Power feels right but I've been babying it. However once it gets to full temp it won't idle at ALL. As soon as you let off the gas it dies instantly. I have to hold the throttle open slightly to keep it idling. It always starts right back up though.
Good battery
New plugs
Original coils and caps
Charlie's place ignition (just timed obviously)
Freshly rebuilt carbs (3D, 26mm float height)
Idle mixture screws at 3/4 (manual spec)
Here's a pic of the plugs after about 20 miles.