Keihin FCR-MX Accelerator Pump Covers

Accelerator Pump Covers 101. Aftermarket covers have a more evolved design that purges air better then the stock cover so there is less hesitation. Note: Most of the aftermarket accelerator pump covers have a smaller capacity because they were designed prior to leak jets so there was no other way to adjust the amount of fuel. You also have to remember that the stock covers are the same for one cylinder as they are for multi cylinders, that is why the aftermarket ones have less of a capacity, 1 cylinder does not need as much fuel as 4 cylinders. The Boyesen Cover has less volume in its void. The R&D Cover is similar to the Boyesen but also has an adjustable leak jet circuit included.