Detonation. See if the clacking gets better with high octane gas.


B. Alexander wrote:
Hi,
I have a mercruiser 3.0 with an Alpha 1 outdrive. the engine runs great up
to about 3/4 throttle, but when I go to w.o.t. the engine still runs fine
but it starts to make a loud clacking sound. I sat beside the engine with
the cover off while someone else was driving to try to determine if it was
caused by something vibrating, but it appears to be coming from inside the
engine. Any ideas what this might be?
Thanks,