Johnson Evinrude Outboard Motors 1956-1970 1.5-40hp repair manual., Page 25Get this manual
2 TUNING 2-1 INTRODUCTION The efficiency, reliability, fuel economy and enjoyment available from engine performance are all directly dependent on having it tuned properlyThe importance of performing service work in the sequence detailed in this chapter cannot be over emphasizedBefore making any adjustments, check the Specifications in the AppendixNEVER rely on memory when making critical adjustmentsBefore beginning to tune any engine, check to be sure the engine has satisfactory compressionAn engine with worn or broken piston rings, burned pistons, or badly scored cylinder walls, cannot be made to perform properly no matter how much time and expense is spent on the tune-upPoor compression must be corrected or the tuneup will not give the desired resultsThe opposite of poor compression would be to consider good compression as evidence of satisfactory cylinderHowever, this is not necessarily the case, when working on an outboard engineAs the professional mechanic has discovered, many times the compression check will indicate satisfactory cylinder, but after the head is pulled and an inspection made, the cylinder will require service