Update on progress:
Got the starboard engine back flushed and got all the pieces of the impeller. Engine was definitely started dry, impeller housing had impeller cooked onto the inside. Flushed the risers good. Got new impeller housing and impeller installed with new sea/fuel pump.

Port engine just got the sea/fuel pump off, and haven't gotten the impeller apart yet, looked thru the hose connections and impeller looked fine but will break everything down for further inspection tomorrow. Something has got to be making the port engine hot as well.

Will also try and pull a plug or two and see color.

I would back flush the port just like you did on the starboard.

BTW

Most pick up the water pressure from the block drains, is that where your gauges hook yup to?


As for jetting did you add power when you rebuilt?

same jetting as before?

Water pressure does hook up at the blocks. Suppose to have gained around 75- 100 hp per engine with the roller cam, lifters, roller rockers, intake. Used the same merc 750 cc carbs from original 454 mags that were on engines. Engines didn't stumble when run up to 4800 rpm. What do I need to look for plug color wise to tell if run lean?

Update: Flushed all engines, pretty confident no blockages, all new impeller housings and impellers (port impellor still looked new) Started inspecting the black exhaust hose, it has all shrank in diameter cutting off the water flow around the riser tips. Ordered stainless exhaust tubing that is similar to the quick and quiet II that I removed. Thought about shooting exhaust with IR gun when completed to check exhaut or tubing temp. What tubing or exhaust temp could I see and it be acceptable (I have read 180*-500*). Am I on the right track to solving this?

Any link to where you purchased this or pictures of it? Is it flexible?

Look for 4" stainless exhaust tubing (straight runs) on jegs, ordered the rubber couplings from laboatparts on ebay.

Update: Got the rubber hose off all the risers. Each hose was touching the flared end of the riser's tail and this is where the burn thru occurred. Got one stainless piece installed between the riser and offset to the tip.

What did the riser gaskets look like

They looked fine to me, there is less than 3-4 hours on these new exhaust manifolds and risers. Is there something I need to pay attention with the gasket?

Just wondering if they were burnt and if the water holes lined up between manifold and riser.