Re: 72 100hp evinrude
That engine will run fine at idle on 2 cyls. As soon as you put it in gear (load up the engine) you will see any real problem. Possible that the engine is not firing on all 4 cylinders. Check spark when the engine is under load (idling in gear at the dock) by putting an inductive timing light on each plugwire. The flashes from the gun will show weak spark, no spark, and misfires. Does the engine run ok at higher rpms?