Engine pulsating

craigswardmtb

Somewhat tough to describe but my port merc 496 seems to pulsate at plane speed rpms. This ultimately leads to some/little vibration. It is not dramatic but certainly sounds different from its starboard sister. I don't feel it in the wheel at all but rather only hear it. Nor does the tach indicate any sort of revving. We were cruising home this morning at 3500 rpms and my wife could simply hear the constant pulsating.  For her to notice the noise it simply made me concerned. I am so anal that I notice everything, so despite hearing "something" most of last season and early this season I thought this to be nothing. Based on the noise you would think the tach would be jumping but it doesn't. It may do it at lower rpms as well but I only audibly notice it when at plane speeds. Any ideas?

some history, the drives (bravo 3) have been well maintained over the years. New oil every season and only 425 hours over the 10 years in service.  The bellows and gimbal bearing was changed 2 seasons ago. The alignment and gimbal bearing were checked this spring.  New drive oil every fall. This year it got new oil fall and spring.  Engine is similar. New oil every season and we do 50-75 hours most seasons. 

craigswardmtb

I changed the plugs last season. I have never changed the wires nor do I see it on the prior owners service records. I might as well if you think it may be a possibility to the issue. 

zaverin1

Well if you had diesels with drive showers then nothing like this would ever happen.

zaverin1

Start with wires and plugs 
look at the coil also 

F1100

Check your engine mount on that engine. Did your prop hit anything? and a chunk is out of it?

is it a vibration? or just a harmonic sound?

BigWeekend88

Marine wires are solid core and do not need to be replaced unless theyre broken or frayed. Cap, rotor, and plugs would be where i start. could simply be a worn  or cracked cap assy... hope that helps