Noise in 3.0l mercruiser

[snake91876]

i hear a noise in my 18' bowrider with newly rebuilt 3.0l mercruiser around the coupler or back of the motor like a clacking , its hard to describe its like a spark knock sound or something . the noise is mostly at wide open throttle which i believe i am too high on my rpms, they are around 5000 and im only getting about 31 mph. it is an old imperial 18' bowrider that the foam in is new so i know its not waterlogged. it has one seat on one side and a back to back seat with a plywood motor cover. does this seem normal, could the noise be in the coupler, u joint, i have new bellows fresh inspected u joint and greased or could it be in the drive unit.

 

[Don S]

Re: Noise in 3.0l mercruiser

It could be anything, even an ignition miss at high rpm. First thing you want to do is get it propped right so you get the rpms in the proper range for your engine. Your speed will come up and your rpms will come down.
Visit the prop forum for details on the prop.
After getting it propped correctly, see if you still have the noise.