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1986 DT 150 runs fine but does get over about 3500 rpms. Its on a Stratos bassboat so that puts me at about 38 mph max. I bought the boat from the original owner who was about 85 years old and he probably didn’t drive it any faster than that. I rebuilt the carbs and fuel pumps. Replaced filters and fuel lines. Changed to a smaller prop. Then bought a new compression gauge and found compression was down to 75 psi. I figured I had found the problem so I rebuilt the whole engine. New pistons, wrist pins and bearings, main bearings, checked all clearances fired it up and nothing has changed. I am beside myself trying to figure out whats wrong. I am a retired mechanic (not an outboard) so I have lots of tools, equipment, and experience but I am stumped. Ready to sell the whole boat motor and trailer. Any ideas?