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Oil Pump

The oil pump is a plunger type of pump, which supplies oil to lubricate the cylinder, piston, and crank chamber parts by pumping oil from the oil tank to the fuel/air mixture being drawn into the engine from the carburetor. In this type of lubrication system, called the Kawasaki Superlube System, the oil pump output is controlled to regulate the ratio of oil to fuel/air mixture so that proper lubrication is achieved at all engine speeds and loads.

The oil pump output is controlled partially by the number of plunger strokes. The number of plunger strokes is determined by the speed of oil pump rotation. Since crankshaft rotation is transmitted through the primary gear, input drive gear, and to the oil pump drive nut, the oil pump output changes in direct proportion to engine r.p.m. While the transmission is in neutral, the oil pump turns all the time. When the transmission is in gear, the oil pump turns only when the motorcycle is in motion.

The other factor that controls oil pump output is the plunger stroke length. This length is determined by the oil pump cam position, which is controlled by the throttle grip through the throttle grip and oil pump cables. As the cam is turned from minimum to maximum flow, plunger movement increases. A greater plunger stroke will pump more oil. Since the throttle grip cable, which pulls on the oil pump cable, is also connected to the carburetor cable, the oil pump output changes with the throttle valve opening.

The oil input to the pump is supplied by a hose from the oil tank, and the output from the pump goes through the output hose and then into the non-return check valve at the banjo bolt connection on the carburetor holder. The oil under pressure, opposes the spring tension on the ball that blocks the valve inlet, flows through the valve and is then ejected through a nozzle into the fuel/air mixture from the carburetor.

The oil pump is designed so that, at zero throttle when the pump is functioning properly, the oil pump lever mark aligns with the mark on the lever stopper, and both the oil pump output that is dependent on the length of the plunger stroke and the throttle valve opening are at their minimum. From this base position the pump lever and the throttle valve move at the same rate as the throttle opens. Any disturbance in this relationship will make the oil pump output too high or too low in relation to the throttle valve opening, resulting in poor performance and spark plug trouble from overlubrication or piston seizure from underlubrication.

Pump malfunction is generally caused by a deteriorated or damaged O-ring or oil seal since the other oil pump parts, being well lubricated by the oil passing through the pump, wear very little and seldom become damaged. A defective part reduces oil pump performance, resulting in underlubrication. Also, air trapped in an oil hose or the pump itself or a clogged check valve obstructs the flow of oil and results in underlubrication.

Any good quality 2 stroke engine oil that is recommended for air cooled engines may be used for the Superlube System. Some other type of oil, such as ordinary motor oil or transmission oil, is not acceptable as a substitute for the proper oil. Poor quality or the wrong type of oil may cause serious engine damage.

Bleeding the Oil Pump

When either of the oil pump hoses has been removed, air may become trapped inside, which will obstruct oil flow. See that oil flows from the inlet hose before reconnecting it to the pump. Bleed the air from the outlet hose by idling the engine (below 2,000 rpm) while holding the oil pump control lever fully open by hand in order to maximize the plunger stroke. Keep the engine idling until the air is completely pumped out. If air bubbles continue to appear in the output hose, check the oil hose connections at the pump.

Oil Pump Performance Test

If a drop in oil pump performance is suspected, check the rate that the oil is being pumped.

•    Remove the oil pump cover.

•    Detach the banjo bolt from the carburetor holder, and run the outlet hose into a container.


•    Attach an instrument for measuring engine rpm to the magneto end of the crankshaft, and start the engine. Using the throttle grip friction adjuster, set the engine at 2,000 rpm.

•    Holding the oil pump lever fully open by hand, collect the oil that is being pumped for 3 minutes. If the quantity of oil collected corresponds to the value the table shows, the oil pump is operating properly.

Oil Pump Output

Output/3 minutes at 2,000 rpm should be 1.4 – 1.7cc

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