I have a 1979 80hp, serial #5141843 that was had what sounded like a deep upper-end knock. Checked timing, all cylinders were firing well...but it still knocked really bad. Really low power in the water. I tore into it, checked connecting rods, wrist pins, all bearings, crankshaft journals..everything appears to be ok. Any suggestions on tests/diagnostics? <br /><br />Also, just bought another motor serial #3753230, was told it was around a 1974 850 Merc. According to the serial numbers on the parts list, it has a distributor; but it has a lightening distributorless ignition system. Looking at both motors, they look identical. Do you see any problem with swapping the powerheads on these motors?
