Wanted to solicit a few opinions on this one. I recently performed ower unit service w/impeller replacement on 81 crossflow engine. Everything appeared to work properly at the house on the hose when I tested her after the job...strong water flow out the pisser and lower unit. Splashed the boat to go for an evening cruise and in the amount of time it took me to park the trailer and walk back to the boat the overheat alarm was going off. turned off engine immediately, raised lower unit to make sure there was no bag or other obstruction preventing water flow, put it back in the water and started engine. She cooled off immediately and stayed cool the rest of the trip. HOWEVER....she is definitely not quite as smooth at idle speed as she was pre-overheat. engine vibration doesn't seem to be as balanced, she's sneezing a tiny bit, and she shakes or sputters a little bit more than before. She still gets on plane at about 3500 rpm which is the same as it always has been, and maxes out at about 5200 RPM (I believe she topped out at 5400 or 5500 before) and sounds good when cruising. Cylinders still have the same compression they've always had, and nothing else seems to be out of place. Have tried to tweak the timing a bit but no improvement. Should I just assume that the overheat warped something inside just enough to make her less "happy" at low idle? Perhaps filler block assembly thereby providing unbalanced routing of exhaust gases? Any other tests I can run before I open the exhaust housing?
