I am about to buy a 75hp mercury that has a pretty rough idle. It idles at 700-750 RPM. When placed in gear the idel becomes slightly rougher but now with a knocking type sound. When increasing rpm to about 1000 to 1100 all goes away, rapid acceleration is good up to 5100 rpm. Just this noisy and shaky idle. Running at any speed above 1000 rpm appears good. I have never owned a mercury before and need to know if this is normal.
