Pull the plugs and see what is going on in the cylinders

Number Eight Plug
Its a Spark Plug
All the eight plugs look like this (Rich)

All good with the plugs. Running rich but not a single plug that looks steam cleaned or new, which is a good sign for valves and the cylinder walls. It also means there is not a head gasket or water intrusion into the cylinder that way. It also means that there is a good possibility there is a crack in the lifter valley or water intrusion into the crankcase from some other means. I’m still going to do the leak down test. I also found the firing order for the engine, so I know what wire goes to what plug.

I verified as I removed each plug that it corresponded to the correct location on the distributer. Yes it a Chevy/GM , even though Sea Ray has a Mercruiser 5.0. This is an Alpha Drive too. My research seems to indicate that the motor is a 2006 /2007 305 GM Vortec. The main difference is the Camshaft duration & lift, the intake and exhaust manifold. This is a Multiport fuel injected motor and the intake seems to be a Mercruiser/Mercury specific item. It seems to be a thousand dollar part. Nothing I’m going to find this at SBT (Short Block Technologies), where I get most of my parts for me Sea Doo’s.

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