Re: "Newer" 25/35hp OMC compatibilities

[Don]

OK, so the gearcase was off. There is a long inner exhaust snout that goes half way down inside the exhaust housing, no real restrictions, so I really don’t think a plugged exhaust is an issue. I’m guessing that the stuff in the cooling system is more like plain mud/sand, and that the previous owner ran the engine through muddy bottom to plug up the passages this way. The gearcase was removed from the engine probably due to previous attempts to unplug the cooling passages.
Can you loosen the telltale elbow easily? If you can, I would simply remove the elbow and run the engine, this will allow all the debris to spill out of the manifold. Again, don’t force that elbow and break it off in the exhaust cover.