My 1982 XT200 has stock exhaust and air filter. The jetting is basic Yamaha specs. The carb has recently spent time in ultrasonic bath with solution of carb dip and water. Fuel level in float bowl seems to be spot on.

The bike idles fine and runs well at higher RPM. The problem is running at low RPM, say 2,300 a 2,800 RPM. The bike will run fine for about 30-40 seconds at this speed then die. This can be replicated consistently.

Thoughts?