1970 60 HP Knock

[Titans Fan]

I have a 1970 60 HP Johnson Outboard. The motor runs fine, planes fine and idles fine. I have replaced the drive shaft. When on the water, at slow idle the motor does great. When I go to WOT I get a knock in the motor like it's slipping out of gear. It will run for fine for a few seconds then a knock (bam).
When it does knock the motor will jump forward slightly, like your pulling it up out of the water.

Can this be a spun hub? I did have a the thrust washer on the wrong end of the prop. (the nut end). I removed the prop and moved the thrust washer to the motor side of the prop at the thrust bushing. Re-installed the prop and tighten the prop nut down really hard with a board holding it while tighting it.

Is the knock(bam) a spun hub or something else? It will do as this run, run, run for about 20 sec. Then bam for about 1 sec. Run, run, run for about 20 seconds then bam for 1 sec. All of thgis is while on plane at 24 MPH.

Any suggestions as to what I should check?

 

[Boobie]

Check the forward gear and clutch dog. Sounds like it's slipping.

 

[bill_w]

If I'm right, the 1970 motors were electric shift. Me, I'd try a different prop, and also drain and refill the gearcase with Type C oil.

 

[Boobie]

Even though it's an electric shift, you can still have a bad gear and dog. That spring can only hold so much.