my sons 125cc quad will start and idle nicely. When you slowly bring up the Rpms its fine. When you give it a burst it stalls. I raised the idle speed and it seems a little better but still does it. I've closed the carb a bit and it is better. This issue started when I went from 87 octane to 93. Has anyone had issues like this.

 

Most likely a partially blocked jet. When accelerating, an engine needs a slightly richer mixture (hence accelerator jets on more expensive carbs) so, if a jet is slightly blocked, the weak mixture will show up when the engine is accelerating.

 

Sounds like fuel/air mixture is off. You can adjust it on screw.