Did you ever change the spark plug.
I remember on my 2 stroke bikes when the plug went bad it would start and idle but die when the throttle was opened. Put a new plug in and it would run like a champ. I always thought that was weird to start and idle fine but die with added throttle.
Stepping back and looking at the overall situation. You said it wasn't sudden, started acting up. Being in Mexico I would think bad fuel or dirty fuel clogging the carb or tank. Did you ever try to start it with the fuel cap off or opened. A clogged gas cap vent can cause fuel starvation.