exhaust manifold leak at the head. bad exhaust gasket,not the riser

sure its not something in the drive

I was going to say check the drive as well. Had mine do the samething, took forever for me to think it could be the drive. Crank it up and put your hand on top of the drive if you fell it knock or tap could be the problem.

Do you have Corsa Captain's Call? The diverters can also make a ticking noise.

No, I just have thru transom exhaust--not captains call. The drive was replaced 2 years ago and functions perfectly. Im going to pull the valve covers next weekend and see whats going on. My best guess is rocker, pushrod, lifter or valve. The tapping noise changes with the rpm's of the motor.

Here's a video of the problem...Im going to pull the valve covers later this week but any opinions would be appreciated

http://www.youtube.com/watch?v=K7Z8I0CvEVs

That sounds alot like the problem my starboard 502 is having. Mine is in the shop and I should be getting a call this week with what they think the problem is.

If you can do the work yourself, you can pull the drive, put a water hose right into the water pickup at the helmet and elemenate the drive as a noise. After that it sounds like you lost a valve seat. Mine did it last year and it still seemed to run good, But it was down on power a little. Good luck, But do the easy stuff first !!

Did you ever hear back from your shop? Im getting alot of people telling me that sounds like a bent pushrod. Im pulling the valve covers tomorrow to have a look.

--Will a bent pushrod be obvious or will I have to loosen the nut on the rocker and pull each pushrod out? Any special knowledge I need to have in regards to pulling them or putting them back? Will the rockers need adjusting after I do this?

Not yet. I am going to call them tommorow. I am not mechanically inclined when it comes to engine building so I leave that up to the mercury techs at the marina. Our intitial thoughts were a bent pushrod or loose rocker arm.

All of my engine temps (water and Oil) as well as pressures were OK. Still had all the power just a knocking/tapping noise. Mine sounds just like yours though and it is very hard to tell where it is coming from. I listened to it in the water and on the trailer. It was louder on the trailer but I expected that.
They were going to pull my covers first to see if they could find the problem there before tearing it apart anymore.