Re: johnson 5 1/2 hp 1956
First off, are you running 24:1 gas to oil? These are bushing engines and they require heavy lubrication. They will lock up if you try and run them on 50:1.
Otherwise I would suspect the engine block has water circulation problems. Mine had a plugged up main passage where the water comes into the block, it turned out to be a paper tower or newspaper that got shredded by the prop, most likely when it was being run in a trash can. I did not see this until I had the power head off while re-painting the engine. Had I run it, I'm sure it would have over heated. Find the problem because these engines tend to break the aluminum connecting rods when they sieze, often breaking the block as well.
