350 MPI running very rough, will not idle, loud tap

You could always try these stainless steel manifolds. I've only had them on for a short time but they seem to work very well. They were about the same costs as MErcruiser OEM dry joint manifolds, spacers and risers.


SS Manifold 2.jpg
 
Bucit said:
You could always try these stainless steel manifolds. I've only had them on for a short time but they seem to work very well. They were about the same costs as MErcruiser OEM dry joint manifolds, spacers and risers.


View attachment 25001
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Well, you got me thinking.. Are yours the Hi-Teks?

http://www.hitekmarine.com.au/

I sent a inquiry into them to get a price; because they are real headers, looks like you get a little HP out of it in addition to potentially forever solving the "rot" problem of the cast iron. I'll let you know when/what I hear back from them; they look expensive, but I hear others saying they aren't much (or any) more than the dry joint cast iron system (which, if it's the case, points to the absolutely obscene profit on the cast iron manifolds).
 
Puma said:
Well, you got me thinking.. Are yours the Hi-Teks?

http://www.hitekmarine.com.au/

I sent a inquiry into them to get a price; because they are real headers, looks like you get a little HP out of it in addition to potentially forever solving the "rot" problem of the cast iron. I'll let you know when/what I hear back from them; they look expensive, but I hear others saying they aren't much (or any) more than the dry joint cast iron system (which, if it's the case, points to the absolutely obscene profit on the cast iron manifolds).
Click to expand...

In case anyone wonders, the HiTeks are about 2500 for my boat. I'd be all over them at that price; however, they have a 4-6 week timeline before they can get them to me. No way I'm going to be without my boat until mid-June/July, so stock Merc it will be for me. The next time, I'll go with the stainless for sure; another 500 bucks to not have to really ever worry about this again (and, a little free HP to boot) seems like a deal to me!
 
Someone may have stated this already so sorry for the repeat if so.
Water or fuel on top of the piston can cause a bent rod with no sign of damage to the top end of the piston. Take Ron's advice and measure the piston TDC against the others.
 
OldSkool said:
Someone may have stated this already so sorry for the repeat if so.
Water or fuel on top of the piston can cause a bent rod with no sign of damage to the top end of the piston. Take Ron's advice and measure the piston TDC against the others.
Click to expand...

I'll ask my mechanic, but, I think in his view, we might as well try the new heads (and then do a compression test) because, if there is lower end damage, the engine has to come out of the boat anyway. But I'll ask him if he has the tool, might save us the work of putting the heads back on just to tear them off again if the compression test doesn't come back good.

Thanks!
 
Puma said:
I'll ask my mechanic, but, I think in his view, we might as well try the new heads (and then do a compression test) because, if there is lower end damage, the engine has to come out of the boat anyway. But I'll ask him if he has the tool, might save us the work of putting the heads back on just to tear them off again if the compression test doesn't come back good.

Thanks!
Click to expand...

Just wanted to update the thread, exhaust replaced, valve job done (and head machined to repair damage) and everything is back together. Compression is good (it was the valve causing the low compression) so no apparent damage to the lower end of the engine. Dodged a bullet on that one. :)
 
Great news!!!!! Go and enjoy the summer!
 
Look closely at the piston Crowns (tops) on those 2 cylinders for any evidence that either piston isn’t coming to the top of the bore. If either is a tick low, it’s bent a rod. Not uncommon with hydro lock.
 
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