Make sure the exhaust is not plugged with oil. Check the screws on the carburetor manifold. They should be tight. Make sure the gray carburetor gasket is not torn. Check for spark from the spark plug cap.
Mosquito seems to bog down during acceleration or has idle problems.
Two stroke engines are somewhat sensitive to altitude. The yellow mixturescrew on the carburetor can be adjusted for different altitudes. In general turn the screw in for lower altitudes or more top end power and out for more bottom end. If desired the silver screw adjusts idle speed. There is another idle adjust under the black rubber cap where the throttle enters the carb.