i have a 1987 merc 3.0 litre with a recent rebuild on the motor, have have been hearing a ticking sound wich i thought at first was exhaust related so i had the exhaust manifold and arm cheked out all is good . so now i open my valve cover and ajust my rocker arms, but when i put it back on the water the ticking sound is almost gone butt still there if i hit the throttle hard but it goes away!!!now the other fdasy i had it on the water running just great shut it down and it never fires back up, i am thinking that ping noise may have bean a spark ticking sound now cause when i started looking at the wires and they where very worn looked to be very old could bad wires cause this, p.s they carb was leting fuel into the barrels