Need input or suggestions on 250 hpdi exhaust manifold

[cehlert]

Bought a 2005 boat with a 2005 Yamaha 250hp HPDI VZ250TLRD motor on it. I dropped the lower unit to put in a new water pump kit. As I was doing this I noticed the exhaust seal was eaten up so ordered a new one. The housing on the water pump was fine, caught it in time. This morning I looked up into the midsection with a flash light and noticed a bunch of carbon buildup. I reached up with a flat chisel and scraped it out. Then I looked up again and noticed something not right. The exhaust manifold is hanging by a bolt and most of the manifold itself is gone. What are the symptoms of a missing/broken exhaust manifolod? I had the boat out one time for short time and the overheat alarm came on after a brief 200yd run after idling for 5 minutes. The water did not seem to be coming out that great. Went home, took out poppet valve, pretty clean for the most part. So I ordered that water pump kit, the impeller in there seemed pretty good for the most part. I ordered new thermostats. Could the bad manifold cause an overheat issue? The motor sounded fine to me. I've had a 200 yamaha before and the noise from this running did not stand out by any means. Thanks for any suggestions. I did order a new manifold, gasket, etc in case when I take stuff apart up there I need them.

[The Next KVD]

Well Casey I'd suggest you talk to that David Bromenshenkel kid. lol. Anywayz I'm surprised that no one else has any take on this other than what I've been emailing you. Come on guyz the bass season is about to open and this man has an AWESOME boat he needs running. I unfortunately don't have all the answers.

[Mat_HT]

i would think the hole-shot would be noticeablly worse with no tuner. The tuner provides back pressure so the exhaust is not relieved so easily. I don't think it would have any bearing on your cooling issue though....except that the burnt up tuner might be caused by an overheat. We have seen tuners get burnt up when sand or gravel gets sucked up and packed in the adapter plate. Maybe what you have going on here? Worth a look.
The other thing Yamaha says will burn up a tuner is when you have fuel pump diaphragms ruptured and raw fuel is being ran thru the engine and as the engine trys to burn all that excess fuel, it creates a giant fire ball coming out of the bottom of the block.
Hope this helps.