1991 Johnson 70 HP motor dies

[fish4fun42]

Background: Purchased boat 3 years ago with very low hours on motor. After running well for 1 season, had trouble with motor cutting off while under power. Motor would start fine, but would then lose power and die (usually when I was about 5 miles from the ramp). I used a fiber optic scope to view the cylinders and found that number 2 was "galled" near the exaust port. Had power head rebuilt, bored, carbs rebuilt in Summer 2000. I am running fuel stablizer year round. I am having the same problem again (no audible alarm). I have removed and inspected all three carbs. They are clean with absolutely no varnish. The compression in top and bottom cylinders is 120# the middle cylinder is 110#. This motor has a VRO. I have heard that it may be good to disconnect and mix oil/gas manually. Need to know what to try next. Thanks.

 

[Dhadley]

Re: 1991 Johnson 70 HP motor dies

I hope you dont have the same problem again but the 56 cid motors have a habit of running lean in the mid range when you are running at full timing advance but very little fuel. #2 piston seizing is a classic symptom. <br /><br />Richen up the mid range, especially on the middle carb. I usually do all 3. And make sure you are using Champion plugs.<br /><br />Good luck!