I found it. Water in the lower cylinder. That explains how it can have spark but no explosion. I pulled the head and water ran out. Head and gasket look OK. I pulled the exhaust cover and found silicone on the gaskets (somebody got here before me) but nothing obviously wrong. I don't...
I'm stumped. I have a 267H4E that has been pretty good to me but it sat the last year or two and this year, it only wants to run on the top cylinder. New plugs didn't help. Both coils check good. I confirmed both cylinders are firing at the correct time via timing light and mark on flywheel...
Like so many old boats, I have one that I just replaced the transom in and part of the stringers. Off course, the foam in the area is water logged. If it is in the back, it likely is in the front too. This is a 21' boat with massive trim tabs on the back (not original). They're big enough...