Before the problem heres the checks and balances.
I checked compression, 160lbs per cylinder, I rebuilt carbs, pulled lower unit rebuilt water pump, also resealed prop shaft while I was at it.
Hooked up battery turned key the starter engaged but would barely turn the engine. Hooked up jumper cables same result. Removed starter, hooked to battery direct, wasnt extremely strong but seemed adequate. Cleaned all connections, same result. Disassembled starter, brushes were worn about halfway, cleaned armature and brushes, lubed and reassembled. Same result. Pulled spark plugs spun engine over seemed to turn freely, observed spark, very strong and bright blue. Choked engine and continued to turn engine over, it has been sitting winterized for a few years, my thinking was the fuel might free up the engine by washing out the fogging oil. reinstalled plugs same result, the engine turns over very slowly, like a dead battery or a bad starter, I had another starter so I tryed that same result. I am totally lost, what have I missed?
Any ideas would be greatly appreciated.

Thanks