Most racers in the CR125 stock classes use the Pumparound carb system. The purpose of the system is to stabilize the fuel level above the jets in the carb during high-g turns. This helps keep the fuel mixture constant whether cornering or accelerating in a straight line.

The system has a remote mounted pump assembly consisting of two fuel pumps on a common diaphragm chamber and a Keihin PWK or PWM carb without floats. The pumps are driven by pressure pulses delivered through a fitting attached to the engine crankcase. One pump delivers fuel from the fuel tank to the float bowl of the carb through a restrictor pressed into the normal carb fuel inlet. The other pump draws fuel from a pick up tube whose entrance inside the carb is placed at the desired fuel level. The pumps and fuel restrictor are sized to deliver more fuel to the carb than the engine can use, and evacuate the excess fuel through the pick up tube and the pump back to the fuel tank.

The benefits of the system can only be realized if the system is installed correctly. Here are the important installation details for a well functioning system:

• Mount the fuel pump assembly above the level of the pressure pulse fitting on the engine crankcase with the pressure pulse fitting pointing down so accumulated oil can drain out of the diaphragm chamber and back into the engine.
• Route fuel lines so that they are not pinched or kinked when parts of the kart or seat flex during operation.
• The flow volume being returned to the tank from the carb is large because it is the total of the air and excess fuel drawn from the carb. The hole in the bulkhead fitting on the fuel tank must be large enough for the fuel and air evacuated from the carb to flow back into the tank with out restriction.
• The fuel tank must have an adequate air vent. The vent hole should be about the same size as the fuel return hole in the tank.
• Never leave the fuel level in the tank above the inlet to the carb. Fuel can siphon into the carb and fill the engine crankcase.

A simple test to verify that the system is operating correctly is to let the engine idle and verify that bubbles are moving from the carb in the fuel line attached to the evacuation tube on the carb.

If all these criterion are met, the system will function as designed and jetting a stock CR125 for maximum performance will be a snap. For more detailed information about SRS Shifter Kart engine recommendations, call us at 903-769-4140.