ACCELERATOR PUMP COVER
The accelerator pump cover for Keihin carburettors has been designed to help reduce the carburettor’s response delay to sudden gas reopening at low rpm.
What happens when abrupt gas reopening occurs?
When the carburettor’s gas valve is opened abruptly, the column of air in the venturi undergoes a momentary slowdown. This leads to a temporary blockage of fuel delivery, with the result that the engine "hesitates" until the increase in engine speed is able to accelerate the column of air necessary to draw fuel through the atomizer and the main jet.
How to avoid this problem?
The accelerator pump guarantees a greater amount of fuel close to the venturi and allows the engine to overcome this stall condition by increasing the rotation speed until the maximum circuit works correctly again.