40 hp Johnson blogs down under a load

by Jake
(Crofton ky)

I have 40 hp Johnson outboard that began to lose power when running on plane last year. It’s like the fuel line would become clogged or something. It wouldn’t die, just slow down to a little above idle speed. When I was running down the lake. Took the hood off and saw leaking around the fuel pump. Ordered a rebuild kit and rebuilt it over the winter. Took it out this year and it will barely get above idle. Runs rough, and won’t open up. Took it back home, went through the pump again to make sure I put it together right. Everything looked good. Replaced the spark plugs and took it back out on the water. Took off good opened up for a few seconds and then went back to bogging under a load again. Turned the motor off and fished with the trolling motor for about an hr, fired the motor back up and it took off again! Only for a few seconds again and then was back to bogging. Took it home, Checked compression on cylinders, both around 120. Checked spark and strong blue streak at 7/16”. Not really wanting to start replacing parts so I came here. Any help would be greatly appreciated.

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