Metering Oil Pump

Metering oil pump regulates the amount of oil pumped to float chamber of carburetor. The oil enters combustion chamber with air/fuel mixture to lubricate seals within chamber. Amount of oil increases as engine RPM increases and the control lever is actuated by a rod connected to throttle lever. Before measuring output, check clearance between metering pump lever and washer as shown in Fig 1. Clearance should be no more than 0.04" (1.0 mm). To check oil discharge, proceed as follows:

Disconnect connecting rod, then disconnect oil lines at carburetor. Start engine and adjust idle to 2000 RPM. Once oil flow from hoses becomes steady, measure volume discharged. Pump should discharge 2.0-2.4 cc in 6 minutes.

Fig 1: Metering Pump Control Rod Adjustment
Courtesy of MAZDA MOTORS CORP.

NOTE: As carburetor will not be receiving oil during test, add a small amount of clean oil to carburetor to provide proper lubrication during testing.
To adjust oil metering pump, turn the adjusting screw clockwise to increase flow or counterclockwise to decrease flow. One complete turn will change oil discharge flow by 0.2-0.3 cc for six minutes of operation. Make sure lock nut of adjustment screw is locked, then recheck metering oil pump discharge rate.