My 1971 4 cylinder 80 hp mercury hesitates up through the rpm range then quits. I found that only the bottom plug to be clean even after replacing it with a dirty plug. Sometimes the plug has the milky reidue on it. Compression reading on all 4 cylinders are at 145 psi and have spark to all cylinders. I've read through many of the Q/A on water leakage but I don't know what dierction to take. Whether to replace the seals on the cylinder block cover, exhaust cover or lower seals. I do see water stain on the outside of the bottom plug just above the threads, but no noticiable water leakage. Changing the lower seals look like a real chore since every bolt I undo has broken off in the past and the power head looks heavy. With top cowling off I do see some exaust smoke just below the power head but can't determine the source. What is the right way to approach this problem?
