Mercury 70hp 1988

by John
(Palm Bay, Florida)

Hi, I'm a newer boat owner of about 3 months now. I've been on the water every weekend and as much as possible during the week. When I first bought it, I did some basic maintenance ie: plugs, wires, impeller, thermostat, fuel filter and fuel lines.

The engine has been running well until a couple of weekends ago when it wouldn't get above 3000 rpm at full throttle. I put it in neutral, shut it down, fired it back up and it seemed to be fine and run as normal after that. This happened again last weekend and also today. The problem seems to be getting worse. Today I tried everything to get it to behave and it didn't until I was at my fishing destination maybe 10-15 minutes of travel.

Funny part is, its only once when leaving the dock where I have trouble. The rest of the day it runs normally and jumps right up on plane 5500 rpm, 35 mph. When it clears itself up, you can hear it trying to gain rpm for a quick couple of seconds, then its like someone hits a switch and it runs perfectly. I can shut it down and fish for 5 minutes or 5 hours.... upon restart, its 100% normal and runs like it should. Its always easy to start, fires right up and idles pretty smoothly. This is the case weather having the issue or not.

It always has no trouble revving in neutral while experiencing its "episodes". Seems to be only under load and only after the first start of the day. Where is a good place to begin testing things? I do have an appropriate Seloc manual.