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With 40 PSI compression in one of the cylinders, I’m not sure if the motor will even run. My first thought is a blown cylinder head gasket. Is there any sign of a breach in the old gasket? Is there any sign of overheating such as burnt/discolored paint on the cylinder head.
A new head gasket is fairly inexpensive for this model, and easy to replace.. If you decide to replace it, then there is a very easy lapping procedure that will give a fresh, new, and flat mating surface. I make it a habit to always lap the cylinder head when installing a new gasket. Every one that I have ever lapped is slightly warped in a concave manner in the direction of the block. I’m hoping this is your solution.
Let us know what you decide to do.
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