No, I havent replaced the IAC yet.
I have changed the sparkplugs.

Took the endpipes away from the boat yesterday and tested if they leak water.
But it was dry... So the only thing left that causing the water leak problem is reversion.

Now I must figure out how to prevent the reversion of the water...
Dry pipes ore make it difficult for the water to reverse back to the engine..





I dont really know what the knocking sound is related to. I bought a stethoscope and listened to the engine and what I could hear there was no sound in the engine. But back at the transom I heard a knocking sound...

I have plans to make a vertical ”wall” inside the beginning of the endpipe.
Like this, but on the other side.




Here:






To prevent water from reenter the exhaust. And to destroy the exhaust pulse.
Thoughts?

I have never heard of reversion in a 496mag if untouched. I´m not an engine guru but I think the cam is to mild to cause any reversion. Have you pressure tested the header itself? If not take them off and pressure test with water and check the runners for leaking water. I fried my CMI´s (its in another thread) and I´m still not sure why it happen.If you have water in one or several cylinders then it can be the water that is causing your idling problems.

I agree with the above ^^^^ I wouldn't dam off or restrict the exhaust flow, Id think you will cause yourself more issues, as stated above pressure text the headers, thats a severe angle on the tail pips dont see how the water would crawl up it.

I have pressure tested the headers with no leaks what I could see.
I also pressure tested the tailpipes yesterday with no leaks.
But maybe I did the pressure test wrong, I dont know. But I didnt see any leaks.

I think my 496 Mag is upgraded to a HO.
Whipple stage 1, headers and maybe another cam.

Okey, I was told the exhaust flow will be higher and different. That it will prevent any reversion