1991 Johnson/Evinrude Models "EI" 40 thru 55 Service Manual, Page 243Get this manual
Jet Drive Adjustments Impeller Clearance Adjustment If loss of performance combined with higher than normal wide-open-throttle RPM is noted (or the RPM limiter actuates), check for wear between the impeller's edge and the water intake casing linerAccelerated impeller wear can occur when operating in waterways which have bottoms composed largely of sand, silt, and gravel
rv liner, check clearance betweenthrough the and intake casing 1To the impeller place feeler gauge intake grille and
measure the clearance between impeller's edge
Impeller Clearance 0.020 in(0,5 mm) Minimum to 0.030 in(0,8 mm) Maximum
PCE0084
2If clearance is more than 0.030 in transfer appropriate number of shims from below to above the impellerThis will move the impeller down and decrease clearance Moving one shim will reduce clearance approximately 0.004"