MS 192 TC starting problems when mildly warm

[GearHead36]

Oh well I thinking the OP used the Stihl's gasket and diaphragm kit which has no inlet needle valve. It so it sounds like a leaky one that is leaking under fuel tank pressurization. If so then the OP needs the Zama RB-69 full carburetor repair kit as the needle valve tip is probably ringed worn.

I replaced the needle valve. The old one looked good, but my eyes aren't good enough to see microscopic wear, and since I had a new one, I replaced it.

 

[GearHead36]

I chased a very similar problem on an old leaf blower once. And it turned out to be the main fuel line from the tank to the carb. When it was cold, the line was fine. But after the engine ran for a bit and everything got warm, the old rubber line would get a little too soft and could collapse or get a tiny air leak when I tried to start it. It wasn't getting enough fuel. A new fuel line for a couple of bucks fixed it completely.
It might be something to check next time it acts up. When it's warm and won't start, just take a quick look at that fuel line to see if it looks soft or pinched.

This sounds like the most likely cause. I'll have to check that. I seem to remember from when I rebuilt the carb that the fuel line was molded. Is that the case? Or will generic fuel line work?

 

[GearHead36]

Thanks, everyone for the suggestions.