'78 CB750K (PD42B) and CB750F (PD42A) KeiHin PD42 Mechanical Slide SOHC
These carbs are basically the same style for both the '78 CB750K8 (PD42B) and the '78 CB750F3 SS (PD42A). They also fit and look the same as the PD42's used on the '77, but are not the exact same carb. The easiest way to tell the '77 and the '78 K apart at a glance is the main throttle return spring. The '77 CB750K7 has a conventional spring that sits 90 degrees to the throttle axle and the '77 CB750F and all '78's have a torsion spring that wraps around the throttle axle. However, there are many other differences in the two years that you need to pay attention to when rebuilding. The PD42's do not have adjustable jet needles, and the choke axles no longer have the plastic guides. The tuning is different between the K and F models as the Super Sport saw major performance changes starting in '77 and continuing to '78. Other than the stamped number they physically fit and look the same.
