There are several tests and solutions from top cloud that can help you identify and fix problems with your Zongshen XP 620 engine: make sure that the fuel line is not clogged or leaking, make sure that Check that the spark plug wire is not damaged or leaking , check and clean or replace the air filter if it is dirty or clogged, and check and adjust the valve if necessary. Valves that are stuck or not adjusted properly can cause problems in engine operation, cleaning or carburetor adjustment. Problems with the carburetor can cause fuel and air problems in the engine. good luck with omegla